Transmission device, reception device, and radio communication method

ABSTRACT

A transmitting apparatus includes an OFDM modulator that generates a first modulation symbol by modulating a first information signal using a first modulation scheme, a signal point of the first modulated information signal being arranged at a first position in an in-phase quadrature-phase plane and a second modulation symbol by modulating a second information signal using the first modulation scheme, and by changing a second position at which a signal point of the modulated second information signal is arranged to a third position in the in-phase quadrature-phase plane, wherein the third position is different from the first position. An OFDM modulation signal includes the first modulation symbol and the second modulation symbol, wherein the OFDM modulation signal comprises a plurality of subcarriers. A transmitter transmits the OFDM modulation signal.

CROSS-REFERENCE PARAGRAPH

The present application is a continuation of U.S. application Ser. No.13/891,027 filed May 9, 2013 which is a continuation of U.S. patentapplication Ser. No. 13/606,327, filed Sep. 7, 2012, now U.S. Pat. No.8,462,615, which is a continuation of U.S. patent application Ser. No.12/767,117, filed Apr. 26, 2010, now U.S. Pat. No. 8,284,650, which is acontinuation of U.S. patent application Ser. No. 10/485,115, filed Feb.4, 2004, now U.S. Pat. No. 7,724,638 which is a National StageApplication of PCT/JP02/07407, filed Jul. 23, 2002, which claims thebenefit of Japanese Application Nos. 2001-244929, filed Aug. 10, 2001;2001-310777, filed Oct. 5, 2001; and 2002-206150, filed Jul. 15, 2002,the contents of which are expressly incorporated herein by reference intheir entireties.

TECHNICAL FIELD

The present invention relates to a transmitting apparatus, receivingapparatus, and radio communication method used in a communication systemin which a greater amount of data is transmitted in a limited frequencyband.

BACKGROUND ART

An example of frame configuration along the time axis in a conventionalradio communication system is shown in FIG. 1. In FIG. 1, reference code1 indicates data symbols, reference code 2 pilot symbols, and referencecode 3 a unique word. In order to demodulate a signal transmitted from atransmitting apparatus, a receiving apparatus must acquire timesynchronization with the transmitting apparatus. For this purpose, thereceiving apparatus acquires time synchronization by detecting uniqueword 3, for example. Also, when demodulating data symbols 1, thereceiving apparatus compensates for channel fluctuations using pilotsymbols 2.

However, in a conventional radio communication system, since a uniqueword and pilot symbols that carry no information are inserted on thetime axis of the frame configuration, the data transmission speed fallsproportionally.

Thus, the idea has been considered of using a different frequency bandfor unique words and pilot symbols from that used for data, andtransmitting these at the same time as data. However, a drawback in thiscase is that the frequency band used becomes wider. There is also adrawback in that, since a different frequency band from that for data isused, unique words and pilot symbols undergo different propagation pathfluctuations than data, and precision when compensating for channelfluctuations degrades.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a transmittingapparatus, receiving apparatus, and radio communication method whereby agreater amount of data is transmitted without degrading receptionquality using a limited frequency band.

This object is achieved by transmitting a plurality of modulated signalsmultiplexed in the same frequency band. However, a plurality ofmodulated signals are not simply multiplexed, but modulated signals suchthat each signal can be separated on the receiving side are combined andmultiplexed in the same frequency band.

It is proposed that, as this combination, modulated signals in which apreset signal sequence has been digitally modulated, modulated signalsdigitally modulated by means of a spread spectrum system, OFDM-spreadmodulated signals, modulated signals digitally modulated by means of aspread spectrum system using spreading codes with different spreadingratios, OFDM-spread modulated signals formed using spreading codes withdifferent spreading ratios, and so forth, be included in a multiplexsignal and transmitted.

Then, on the receiving side, from within the multiplex signal containingthe above-described modulated signals, the above-described modulatedsignals first undergo correlation processing with a preset signalsequence, despreading processing, despreading processing using spreadingcodes with different spreading ratios, and so forth, and aredemodulated. Next, replica signals of the provisionally demodulatedsignals are formed, and by eliminating the replica signals from themultiplex signal, the other signals contained in the multiplex signalare extracted.

By this means, even when a plurality of modulated signals aretransmitted multiplexed in the same frequency band, it is possible toseparate and demodulate these signals on the receiving side.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing a sample frame configuration in aconventional radio communication system;

FIG. 2 is a drawing showing an example of frame configurations of amultiplex transmit signal according to Embodiment 1 of the presentinvention;

FIG. 3 is a drawing showing 16QAM signal point arrangement in the I-Qplane;

FIG. 4 is a drawing showing BPSK modulation signal point arrangement inthe I-Q plane;

FIG. 5 is a conceptual diagram showing frequency arrangement inEmbodiment 1;

FIG. 6 is a block diagram showing the configuration of a transmittingapparatus of Embodiment 1;

FIG. 7 is a block diagram showing the configuration of a receivingapparatus of Embodiment 1;

FIG. 8 is a drawing provided for explanation of correlation computationby a synchronization section;

FIG. 9 is a drawing showing correlated signal time fluctuations;

FIG. 10 is a block diagram showing the internal configuration of thedemodulation section of FIG. 7;

FIG. 11 is a block diagram showing the internal configuration of thesignal regeneration section of FIG. 10;

FIG. 12 is a drawing showing the spectral distribution of a signal aftercode multiplication;

FIG. 13 is a block diagram showing the internal configuration of thepilot signal estimation section of FIG. 10;

FIG. 14 is a drawing showing the configuration of a radio communicationsystem of Embodiment 2 of the present invention;

FIG. 15 is a drawing showing an example of correlation characteristicsin Embodiment 2;

FIG. 16 is a drawing showing sample frame configurations of a multiplextransmit signal according to Embodiment 3;

FIG. 17 is a drawing showing 16QAM and pilot symbol signal pointarrangement in the I-Q plane;

FIG. 18 is a block diagram showing the configuration of a transmittingapparatus of Embodiment 3;

FIG. 19 is a block diagram showing the configuration of a receivingapparatus of Embodiment 3;

FIG. 20 is a drawing showing the configuration of pilot symbols andsymbols between pilot symbols according to Embodiment 3;

FIG. 21 is a drawing showing sample frame configurations of a multiplextransmit signal according to Embodiment 4;

FIG. 22 is a block diagram showing the configuration of a transmittingapparatus of Embodiment 4;

FIG. 23 is a block diagram showing the configuration of a receivingapparatus of Embodiment 4;

FIG. 24 is a drawing showing the arrangement of a base station andcommunication terminals in a radio communication system of Embodiment 5;

FIG. 25 is a drawing showing signal point arrangement in the I-Q planeof a QPSK modulation signal and n/4 shift QPSK modulation signal;

FIG. 26 is a drawing showing signal point arrangement in the I-Q planeof a BPSK modulation signal and n/2 shift BPSK modulation signal;

FIG. 27 is a block diagram showing the configuration of the spreadspectrum demodulation section used in a receiving apparatus ofEmbodiment 6;

FIG. 28 is a block diagram showing the configuration of a transmittingapparatus of Embodiment 7;

FIG. 29 is a drawing showing sample frame configurations of a multiplextransmit signal according to Embodiment 7;

FIG. 30 is a block diagram showing the configuration of a receivingapparatus of Embodiment 7;

FIG. 31 is a drawing showing another example of frame configurations ofa multiplex transmit signal according to Embodiment 7;

FIG. 32 is a block diagram showing the configuration of a receivingapparatus that receives and demodulates the multiplex transmit signal ofFIG. 31;

FIG. 33 is a drawing showing the configuration of the multiplex signalselection section used in a transmitting apparatus of Embodiment 8;

FIG. 34 is a drawing showing sample frame configurations of a multiplextransmit signal whose constituent signals are multiplexed in the samefrequency band according to Embodiment 9;

FIG. 35 is a block diagram showing a configuration of a transmittingapparatus of Embodiment 9;

FIG. 36 is a block diagram showing a configuration of a receivingapparatus of Embodiment 9;

FIG. 37 is a block diagram showing another sample configuration of atransmitting apparatus of Embodiment 9;

FIG. 38 is a block diagram showing another sample configuration of areceiving apparatus of Embodiment 9;

FIG. 39 is a drawing showing sample frame configurations of a multiplextransmit signal whose constituent signals are multiplexed in the samefrequency band according to Embodiment 10;

FIG. 40 is a drawing showing sample frame configurations of a multiplextransmit signal whose constituent signals are multiplexed in the samefrequency band according to Embodiment 10;

FIG. 41 is a block diagram showing the configuration of a transmittingapparatus that transmits the multiplex transmit signal of FIG. 39;

FIG. 42 is a block diagram showing the configuration of a receivingapparatus that receives the multiplex transmit signal of FIG. 39;

FIG. 43 is a block diagram showing the configuration of a transmittingapparatus that transmits the multiplex transmit signal of FIG. 40;

FIG. 44A is a drawing showing a sample frame configuration of amultiplex transmit signal whose constituent signals are multiplexed inthe same frequency band according to Embodiment 11;

FIG. 44B is a drawing showing a sample frame configuration of amultiplex transmit signal whose constituent signals are multiplexed inthe same frequency band according to Embodiment 11;

FIG. 45 is a block diagram showing the configuration of a transmittingapparatus that transmits the multiplex transmit signal of FIG. 44;

FIG. 46 is a block diagram showing the configuration of a receivingapparatus that receives the multiplex transmit signal of FIG. 44;

FIG. 47 is a drawing showing a frame configuration of a multiplextransmit signal according to Embodiment 12;

FIG. 48 is a block diagram showing the configuration of a transmittingapparatus that transmits the multiplex transmit signal of FIG. 47;

FIG. 49 is a block diagram showing the configuration of a receivingapparatus that receives the multiplex transmit signal of FIG. 37;

FIG. 50 is a drawing showing another sample frame configuration of amultiplex transmit signal according to Embodiment 12;

FIG. 51 is a block diagram showing the configuration of a transmittingapparatus that transmits the multiplex transmit signal of FIG. 50;

FIG. 52 is a block diagram showing the configuration of a receivingapparatus that receives the multiplex transmit signal of FIG. 50;

FIG. 53 is a drawing showing sample frame configurations of a multiplextransmit signal according to Embodiment 13;

FIG. 54 is a drawing showing the symbol configuration of spread spectrumcommunication method A according to Embodiment 13;

FIG. 55 is a drawing showing the symbol configuration of spread spectrumcommunication method B according to Embodiment 13;

FIG. 56 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 13;

FIG. 57 is a block diagram showing the configuration of the spreadspectrum communication method modulation section of FIG. 56;

FIG. 58 is a block diagram showing the configuration of a receivingapparatus according to Embodiment 13;

FIG. 59 is a block diagram showing a configuration of the spreadspectrum communication demodulation section of FIG. 58;

FIG. 60 is a block diagram showing another sample configuration of thespread spectrum communication demodulation section of FIG. 58;

FIG. 61 is a drawing showing signal point arrangement in the I-Q planewhen transmission power is changed every multiplexed signal;

FIG. 62 is a drawing showing sample frame configurations of a multiplextransmit signal whose constituent signals are multiplexed in the samefrequency band according to Embodiment 14;

FIG. 63 is a block diagram showing the configuration of a transmittingapparatus of Embodiment 14;

FIG. 64 is a block diagram showing the configuration of a receivingapparatus of Embodiment 14;

FIG. 65 is a drawing showing sample frame configurations of a multiplextransmit signal whose constituent signals are multiplexed in the samefrequency band according to Embodiment 15;

FIG. 66 is a block diagram showing the configuration of a transmittingapparatus of Embodiment 15;

FIG. 67 is a block diagram showing the configuration of a receivingapparatus of Embodiment 16;

FIG. 68 is a block diagram showing the configuration of a modulationsection, serial/parallel conversion section, and spreading section whena multiplexed signal is composed of a plurality of channels;

FIG. 69 is a block diagram showing the configuration when a signalcomposed of a plurality of channels is demodulated;

FIG. 70 is a drawing showing the positional relationship between a basestation and terminals provided for explanation of Embodiment 16;

FIG. 71 is a drawing showing an example of frame configurations of atransmit signal in Embodiment 16;

FIG. 72 is a drawing showing an example of frame configurations of atransmit signal in Embodiment 16;

FIG. 73 is a block diagram showing the configuration of a transmittingapparatus that selects OFDM modulation signals or OFDM-spreadingmodulation signals according to the radio wave propagation environmentand transmits them multiplexed in the same frequency band;

FIG. 74 is a block diagram showing the configuration of a receivingapparatus that demodulates a multiplex signal transmitted from thetransmitting apparatus of FIG. 73;

FIG. 75 is a drawing showing the frame configuration generated by theframe generation section of FIG. 74; and

FIG. 76 is a block diagram showing the configuration of a receivingapparatus that selects a signal according to the radio wave propagationenvironment from signals which undergo both OFDM modulation processingand OFDM-spreading modulation processing on the same information signaland are multiplexed in the same frequency band.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the accompanying drawings, embodiments of thepresent invention will be explained in detail below.

Embodiment 1

In Embodiment 1, a case is described in which a modulated signal inwhich information is digitally modulated (hereinafter referred to as“information modulated signal”) and a modulated signal in which aspecific signal sequence is digitally modulated (hereinafter referred toas “specific information signal”) are multiplexed in the same frequencyband on the transmitting side, and on the receiving side the multiplexedsignals are separated and the information modulated signal isdemodulated.

FIG. 2 is a drawing showing an example of frame configurations accordingto Embodiment 1. FIG. 2 (A) shows the information modulated signal frameconfiguration when 16QAM is used as the modulation method, with datasymbols 101 comprising 10 symbols. FIG. 2 (B) shows the specificmodulated signal frame configuration, with BPSK modulation used as themodulation method by way of example.

FIG. 3 is a drawing shows 16QAM signal point mapping in thein-phase-quadrature plane (I-Q plane), with reference codes 201indicating 16QAM signal points. Data symbols 101 in FIG. 2 (A) arearranged at signal points 201 in FIG. 3.

FIG. 4 is a drawing showing BPSK modulation signal point mapping in theI-Q plane. Reference code 301 and reference code 302 indicate BPSKmodulation signal points, with BPSK modulation signal point 301coordinates of (I,Q)=(1,0), and BPSK modulation signal point 302coordinates of (I,Q)=(−1,0). Reference code 102 in FIG. 2 indicates asymbol at BPSK modulation signal point 301 in FIG. 4, and reference code103 indicates a symbol at BPSK modulation signal point 302 in FIG. 4. Atthis time, a specific modulated signal frame with which an informationmodulated signal is modulated is composed of five reference code 102symbols and five reference code 103 symbols, as shown in FIG. 2 (B).

FIG. 2 is an example of frame configurations of a radio communicationsystem according to this embodiment, and has, for example, a signal witha cycle on the time axis as a specific modulated signal, with a knownsignal such as shown in FIG. 2 (B) or information, as with spreadspectrum communication, transmitted, but a signal with systematicnessmay also be used within the spreading code cycle. In this embodiment, aspecific modulated signal is used as a pilot symbol.

The way in which the information modulated signal in FIG. 2 (A) andspecific modulated signal in terminal 2B are multiplexed is shown inFIG. 5. FIG. 5 shows the arrangement of an information modulated signaland specific modulated signal, with the vertical axis indicating signalpower and the horizontal axis indicating frequency. Reference code 401indicates the information modulated signal spectrum, and reference code402 the specific modulated signal spectrum. At this time, as shown inFIG. 5, information modulated signal spectrum 401 and specific modulatedsignal spectrum 402 are multiplexed, by which means frequency isutilized effectively.

These signals can be multiplexed in the same frequency band in this wayby making the band occupied by information modulated signal spectrum 401and the band occupied by specific modulated signal spectrum 402 equal.This can be done by making the information modulated signal symboltransmission speed and specific modulated signal symbol transmissionspeed equal.

FIG. 6 shows the configuration of a transmitting apparatus according tothis embodiment. Here, FIG. 6 will be described taking the frameconfiguration in FIG. 2 as an example. In FIG. 6, an informationmodulation section 501 performs 16QAM modulation of an input informationsignal, and outputs an information modulated signal to an additionsection 503. A digital modulation section 502 outputs to additionsection 503 a specific modulated signal that has undergone 10-symbolcycle BPSK modulation on the time axis in accordance with the frameconfiguration in FIG. 2 (B).

Addition section 503 multiplexes the information modulated signal outputfrom 501 and the BPSK modulated specific modulated signal output fromdigital modulation section 502, and outputs the multiplexed signal(hereinafter referred to as “multiplex signal”) to a band-limitingfilter section 504.

Band-limiting filter section 504 performs band-limiting of the multiplexsignal output from addition section 503 by means of a Nyquist filter,for example, and outputs the resulting signal to a radio section 505.Radio section 505 performs predetermined radio processing on theband-limited signal output from band-limiting filter section 504, andoutputs a transmit signal to a transmission power amplification section506. Transmission power amplification section 506 performspower-amplification on the signal that has undergone radio processingoutput from radio section 505, and transmits the resulting signal via anantenna 507.

FIG. 7 shows the configuration of a receiving apparatus according tothis embodiment. In FIG. 7, a radio section 602 performs predeterminedradio processing on a signal received via an antenna 601 (receivedsignal), and outputs the resulting signal to a synchronization section603 and demodulation section 604.

Synchronization section 603 acquires synchronization with thetransmitting apparatus based on the signal that has undergone radioprocessing output from radio section 602, and outputs a timing signal todemodulation section 604. Demodulation section 604 demodulates thesignal that has undergone radio processing output from radio section 602based on the timing signal output from synchronization section 603, andoutputs an information signal.

The operation of a transmitting apparatus and receiving apparatus withthe above configurations will now be described. In FIG. 6, aninformation signal undergoes 16QAM modulation by information modulationsection 501, and is output to addition section 503. A signal that has a10-symbol cycle in accordance with the frame configuration in FIG. 2 (B)undergoes BPSK modulation by digital modulation section 502, and theresulting signal is output to addition section 503.

The information modulated signal output from information modulationsection 501 and the BPSK modulated specific modulated signal output fromdigital modulation section 502 are multiplexed by addition section 503,and the resulting signal is output to band-limiting filter section 504.The multiplex signal output from addition section 503 is band-limited byband-limiting filter section 504 and output to radio section 505. Theband-limited signal output from band-limiting filter section 504undergoes predetermined radio processing by radio section 505, and theresulting signal is output to transmission power amplification section506. The signal that has undergone radio processing output from radiosection 505 undergoes power amplification by transmission poweramplification section 506, and the resulting signal is transmitted viaantenna 507.

A signal transmitted from the transmitting apparatus is received byradio section 602 via antenna 601 in FIG. 7. The signal received viaantenna 601 (received signal) undergoes predetermined radio processingby radio section 602, and the resulting signal is output tosynchronization section 603 and demodulation section 604. The signaloutput from radio section 602 undergoes time synchronization with thetransmitting apparatus by synchronization section 603, and a timingsignal is output to demodulation section 604. The signal output fromradio section 602 is demodulated by demodulation section 604 based onthe timing signal output from synchronization section 603.

The internal configuration of synchronization section 603 in FIG. 7 willnow be described using FIG. 8. FIG. 8 shows the configuration wherebycorrelation computation is performed in this embodiment. In thedescription here, a signal transmitted using the frame configuration inFIG. 2 is taken as an example. A delay section 701 outputs the inputsignal delayed by one symbol. Here, a received quadrature basebandsignal is designated (Ii,Qi), a received quadrature baseband signaldelayed by one symbol is designated (Ii-1,Qi-1), a received quadraturebaseband signal delayed by two symbols is designated (Ii-2,Qi-2), and areceived quadrature baseband signal delayed by n symbols is designated(Ii-n,Qi-n) (where 1≦n≦9).

Signals delayed by n symbols by delay section 701 and the receivedquadrature baseband signal are multiplied by a predetermined constant (1or −1 derived from the symbol arrangement shown in FIG. 2 (B)) in amultiplication section 702, and correlation is established with thetransmitted 10-symbol cycle BPSK modulated signal. The multipliedsignals are output to an addition section 703.

The multiplied signals output by multiplication section 702 are added byaddition section 703, and the added signals (Iadd, Qadd) are output to apower calculation section 704. The added signals (Iadd, Qadd) output byaddition section 703 undergo processing in power calculation section 704to obtain a correlation signal (Iadd²+Qadd²), which is output.

The nature of time fluctuations of the correlated signal obtained bypower calculation section 704 is shown in FIG. 9. The horizontal axisindicates time and the vertical axis power, and reference code 801 showsthe fluctuations. As shown by reference code 801, the specific modulatedsignal cycle has a correlation peak every 10 symbols. The receivingapparatus can acquire time synchronization with the transmittingapparatus by detecting this peak position. Therefore, timesynchronization between transmission and reception can be acquiredwithout inserting a unique word for that purpose. Consequently, sinceUnique words need not be inserted into the information modulated signal,data transmission efficiency can be improved correspondingly.

FIG. 10 shows the internal configuration of demodulation section 604 inFIG. 7. A delay section 901 delays an input received signal by theamount of time taken to regenerate a signal in a signal regenerationsection 902, and outputs the delayed received signal to a subtractionsection 903. Signal regeneration section 902 regenerates a specificmodulated signal from the input received signal based on an input timingsignal, and outputs the regenerated signal to subtraction section 903.The operation of signal regeneration section 902 will be described indetail later herein.

Subtraction section 903 subtracts the specific modulated signal outputfrom signal regeneration section 902 from the delayed received signaloutput from delay section 901. By this means, the specific modulatedsignal is eliminated from the received signal, and the informationmodulated signal only is extracted. The information modulated signal isthen output to a detection section 905.

Based on an input timing signal, a pilot signal estimation section 904extracts the specific modulated signal resulting from elimination of theinformation modulated signal from the input received signal, and outputsthis extracted signal to detection section 905 as a known pilot signalbetween transmission and reception. The operation of pilot signalestimation section 904 will be described in detail later herein. Basedon the specific modulated signal output from pilot signal estimationsection 904 and the timing signal, detection section 905 performsdetection processing on the information modulated signal output fromsubtraction section 903, and outputs the signal after detection.

By using a specific modulated signal as a pilot signal in this way, aninformation modulated signal can be detected without inserting pilotsymbols in the information modulated signal. As a result, data symbolscan be assigned instead of pilot symbols, enabling data transmissionefficiency to be improved.

FIG. 11 shows the internal configuration of signal regeneration section902 in FIG. 10. In FIG. 11, a code multiplication section 1001multiplies the input received signal by a code corresponding to thespecific modulated signal based on the timing signal, and outputs thereceived signal that has undergone code multiplication to an LPF (LowPass Filter) 1002. LPF 1002 eliminates the information modulated signalcomponent from the post-code-multiplication multiplex signal output fromcode multiplication section 1001 (the information modulated signalcomponent in the post-code-multiplication multiplex signal is ahigh-frequency component), and outputs the specific modulated signalcomponent to a re-code-multiplication section 1003.Re-code-multiplication section 1003 regenerates a specific modulatedsignal by performing code multiplication again on the specific modulatedsignal component that has passed through LPF 1002, based on the timingsignal. In this way, a specific modulated signal replica signal isformed.

A received signal that has undergone code multiplication by codemultiplication section 1001 will now be described in detail using FIG.12. A received quadrature baseband signal following code multiplicationis composed of a post-code-multiplication information modulated signaland specific modulated signal. At this time, as shown in FIG. 12, thefrequency axis spectrum of the post-code-multiplication informationmodulated signal is as indicated by reference code 1101, and thespecific modulated signal frequency axis spectrum is as indicated byreference code 1102. Thus, since the frequency of specific modulatedsignal spectrum 1102 is lower than that of information modulated signalspectrum 1101, the information modulated signal component can beeliminated from the post-code-multiplication signal by LPF 1002, and thesignal that has passed through LPF 1002 comprises only the specificmodulated signal component.

FIG. 13 shows the internal configuration of pilot signal estimationsection 904 in FIG. 10. A code multiplication section 1201 performs codemultiplication on the input received signal based on the timing signal,and outputs the post-code-multiplication received signal to an LPF 1202.LPF 1202 outputs only the specific modulated signal component from thepost-code-multiplication received signal output from code multiplicationsection 1201, and uses this signal as a pilot signal.

In FIG. 2, a case is illustrated in which BPSK modulation is used forthe specific modulated signal, but this is not a limitation. Forexample, when a multiplexed specific modulated signal is used as a pilotsignal, use of PSK modulation in which there is no information in theamplitude component in the I-Q plane is an effective means, and theconfigurations of the transmitting apparatus and receiving apparatus areparticularly simple when BPSK modulation or QPSK modulation is used.

In a receiving apparatus of a radio communication system according tothis embodiment, an information modulated signal cannot be demodulatedif the signal sequence of a specific modulated signal to be multiplexedis not known. Therefore, secure radio communication can be carried outby using a multiplexed specific modulated signal as an encryption key.

The specific modulated signal to be multiplexed here has a 10 symbolcycle as shown for instance in FIG. 2 (B), and can be generated in avariety of types. By changing the type of the specific modulated signalto be multiplexed at the transmission apparatus and identifying thespecific modulated signal to be multiplexed at the receiving apparatus,information is in effect transmitted to the receiving apparatus and canbe used as simplified control information for the receiving apparatus.

As described above, according to this embodiment, it is possible toincrease the amount of information that can be sent dependably in alimited frequency band by having the transmitting apparatus transmit aninformation modulated signal and specific modulated signal multiplexedin the same frequency band. Also, it is possible to separate theinformation modulated signal and specific modulated signal from themultiplex signal, and demodulate the information modulated signalcompensating for propagation path fluctuations based on the specificmodulated signal, thereby eliminating the necessity of inserting uniquewords or pilot symbols in an information modulated signal by timedivision, and so enabling the data transmission speed to be improvedcorrespondingly.

Embodiment 2

In Embodiment 2 a radio communication method is described whereby atransmit signal multiplexed according to Embodiment 1 is transmittedsimultaneously by a plurality of stations.

FIG. 14 shows the configuration of a radio communication systemaccording to this embodiment. In FIG. 14, a transmit signal generatingstation 1304 generates, and transmits to a base station 1301 and basestation 1302, a modulated signal with the frame configuration in FIG. 2,for example, and base station 1301 and base station 1302 perform radiotransmission of an information modulated signal and specific modulatedsignal multiplexed in the same frequency band. It is assumed that aterminal 1303 is equipped with a receiving apparatus as shown in FIG. 7,and synchronization section 603 is equipped with a correlationcalculation section as shown in FIG. 8.

As shown in FIG. 14, terminal 1303 receives a radio wave from basestation 1301 and a radio wave from base station 1302. At this time,terminal 1303 can improve reception error rate characteristics byseparating and equalizing the radio wave from base station 1301 and theradio wave from base station 1302. This will be explained using FIG. 15.FIG. 15 shows an example of correlation characteristics when terminal1303 receives a radio wave from base station 1301 and a radio wave frombase station 1302, and performs the correlation computation shown inFIG. 8. In FIG. 15, reference code 1401 indicates the correlationcharacteristic of a radio wave from base station 1301, and referencecode 1402 indicates the correlation characteristic of a radio wave frombase station 1302. As shown in FIG. 15, there are propagation delaysuntil the radio wave from base station 1301 and the radio wave from basestation 1302 arrive at terminal 1303. Reception error ratecharacteristics in terminal 1303 can be improved by equalizing thereceived signals based on the difference in these delays.

As described above, according to this embodiment, when a transmit signalmultiplexed according to Embodiment 1 is transmitted simultaneously by aplurality of stations, reception error rate characteristics can beimproved by having a receiving apparatus that receives multiplexedtransmit signals equalize the received signals.

Embodiment 3

In Embodiment 3 a case is described in which an information modulatedsignal and a modulated signal modulated by means of a spread spectrumcommunication system modulation method (hereinafter referred to as“spread modulated signal”) are multiplexed in the same frequency band,and on the receiving side the multiplexed signal is separated into aninformation modulated signal and spread modulated signal anddemodulated.

FIG. 16 shows an example of frame configurations on the time axis of aradio communication system according to this embodiment. FIG. 16 (A)shows the information modulated signal frame configuration, and assumesthe use of 16QAM modulation as the modulation method. Reference codes1501, 1502, and 1503 indicate pilot symbol fields, each comprising onesymbol. Reference codes 1504 and 1505 indicate data symbol fields, eachcomprising 10 symbols. FIG. 16 (B), on the other hand, shows theinformation spread modulated signal frame configuration. Reference codes1506 and 1507 indicate spread spectrum modulation symbol fields. Whenspread spectrum processing is performed, each field comprises 10 chipscorresponding to 10 symbols. Data symbols and spread spectrum modulationsymbols are assumed to be multiplexed on the time axis.

FIG. 17 shows 16QAM and pilot symbol signal point mapping in the I-Qplane. In FIG. 17, reference code 1601 indicates signal points of thedata symbols indicated by reference codes 1504 and 1505 in FIG. 16, andreference code 1602 indicates the signal point of the pilot symbolsindicated by reference codes 1501, 1502, and 1503 in FIG. 16.

FIG. 18 shows the configuration a transmitting apparatus 1700 accordingto this embodiment. In FIG. 18, an information modulation section 1701performs digital modulation in accordance with the frame configurationin FIG. 2 (A) on an input information signal, and outputs an informationmodulated signal to an addition section 1703. A spread spectrummodulation section 1702 performs spread spectrum modulation on the inputinformation signal, and outputs a spread modulated signal in accordancewith the frame configuration in FIG. 2 (B) to addition section 1703.

Addition section 1703 adds the information modulated signal output frominformation modulation section 1701 and the spread modulated signaloutput from spread spectrum modulation section 1702, and outputs thesignal resulting from the addition (multiplex signal) to a band-limitingfilter section 1704. Band-limiting filter section 1704 performsband-limiting on the multiplex signal output by addition section 1703,and outputs the resulting signal to a radio section 1705.

Radio section 1705 performs predetermined radio processing on theband-limited signal output from band-limiting filter section 1704, andoutputs a transmit signal to a transmission power amplification section1706. Transmission power amplification section 1706 performs poweramplification on the transmit signal output from radio section 1705, andtransmits the amplified transmit signal via an antenna 1707.

By this means it is possible to transmit a modulated signal in which aninformation modulated signal and spread modulated signal aremultiplexed.

FIG. 19 shows the configuration of a receiving apparatus 1800 accordingto this embodiment. Demodulation of 16QAM modulated data symbols 1504and spread spectrum modulation symbols 1506 in the frame configurationsshown in FIG. 16 is described below. In FIG. 19, a radio section 1802performs predetermined radio processing on a signal received via anantenna 1801 (received signal), and outputs the received signal that hasundergone radio processing to a spread spectrum demodulation section1803 and delay section 1806.

Spread spectrum demodulation section 1803 performs spread spectrumdemodulation of the signal output by radio section 1802, and outputs theobtained received digital signal to a spread spectrum modulated signalregeneration section 1805. A distortion estimation section 1804 detects,for example, pilot symbols 1501 and 1502 in FIG. 16 from the inputreceived signal, estimates received signal distortion in data symbols1504 and spread spectrum modulation symbols 1506, and outputs a signalindicating this distortion (hereinafter referred to as “distortionsignal”) to spread spectrum modulated signal regeneration section 1805and an information demodulation section 1808. The operation ofdistortion estimation section 1804 will be described in detail laterherein.

Spread spectrum modulated signal regeneration section 1805 forms areplica signal of the spread spectrum modulated signal by executing thereverse of the processing of spread spectrum modulation section 1702 onthe received digital signal output by spread spectrum demodulationsection 1803. At this time, spread spectrum modulated signalregeneration section 1805 forms a replica signal that includes theamount of distortion in transmission by forming a replica signal usingdistortion information estimated by distortion estimation section 1804.The formed replica signal is then output to a subtraction section 1807.

Delay section 1806 delays the input signal by the amount of timenecessary to generate an estimated spread spectrum modulated signal, andoutputs the delayed signal to subtraction section 1807. Subtractionsection 1807 subtracts the spread modulated signal component containedin the received signal output from spread spectrum modulated signalregeneration section 1805 from the delayed signal output from delaysection 1806, and outputs a received signal from which the multiplexedspread modulated signal component has been removed—that is to say, aninformation modulated signal only—to information demodulation section1808.

Based on the received signal distortion signal output from distortionestimation section 1804, information demodulation section 1808demodulates the information modulated signal output from subtractionsection 1807, extracts information, and outputs an information signal.

The operation of distortion estimation section 1804 will now bedescribed in detail using FIG. 20. FIG. 20 shows the configuration ofpilot symbols and symbols between pilot symbols. In FIG. 20, referencecodes 1901 and 1902 indicate pilot symbols, with pilot symbol 1901 takenas corresponding to pilot symbol 1501 in FIG. 16, the in-phase componentof the received signal (quadrature baseband signal) at this timedesignated Ip1, and the quadrature phase component designated Qp1.

Also, pilot symbol 1902 indicates pilot symbol 1502 in FIG. 16, with thein-phase component of the received signal (quadrature baseband signal)at this time designated Ip2, and the quadrature phase componentdesignated Qp2. If the in-phase component and quadrature phase componentof the distortion signal of first pilot symbol 1901 are designated I1and Q1, respectively, I1=10Ip1/11+Ip2/11 is obtained using Ip1 and Ip2,and Q1=10Qp1/11+Qp2/11 is obtained from Qp1 and Qp2.

Similarly, if the in-phase component and quadrature phase component ofthe distortion signal of the nth symbol (where 1≦n≦10) are designated Inand Qn respectively, In=(11−n)Ip1/11+nIp2/ and Qn=(11−n)Qp1/11+nQp2/11can be obtained. The distortion signal obtained in this way is output asthe received signal (quadrature baseband signal) distortion signal.

By means of a receiving apparatus with the above-describedconfiguration, an information modulated signal and spread modulatedsignal can be separated from a signal in which the information modulatedsignal and spread modulated signal are multiplexed in the same frequencyband. Thus, the data transmission speed can be improved to the extentthat an information modulated signal and spread modulated signal aretransmitted multiplexed compared with the case where these signals aretransmitted independently.

In the case shown in FIG. 18, the pilot signal generation function hasbeen described as being assigned to information modulation section 1701,but this function may also be assigned to spread spectrum modulationsection 1702. Also, as a different method, an apparatus configuration ispossible in which a pilot signal generation section is provided, and thepilot signal generation function is not assigned to informationmodulation section 1701 or spread spectrum modulation section 1702.

The frame configurations are not limited to those shown in FIG. 16, and,for example, pilot symbols need not be inserted. In this case, a pilotgeneration function is not necessary. Also, a unique word, preamble, orother control symbols may be inserted.

In the receiving apparatus in FIG. 19, time synchronization with thetransmitting apparatus is possible by computing the correlation betweena multiplex signal and spread signal, for example, and detecting powerpeaks. This is the same as detecting a spread signal component of amultiplex signal.

The configurations of a transmitting apparatus and receiving apparatusare not limited to the configurations shown in FIG. 18 and FIG. 19.

In FIG. 16, use of a single-carrier method is described for aninformation modulated signal, but the method is not limited to asingle-carrier method, and a multicarrier method such as an OrthogonalFrequency Division Multiplex (OFDM) method may be used. In this case,the horizontal axis in FIG. 16 showing frame configurations may beconsidered to be the frequency axis. Also, a case has been described inwhich 16QAM modulation is used as the modulation method, but BPSKmodulation, QPSK modulation, or the like may also be used.

A case has been described in which the spread spectrum modulation codemultiplexing number is one, but a multiplicity may also be used. Thus,in the transmitting apparatus in FIG. 18, the spread spectrum modulationsection is not limited to performing spread spectrum modulation with onecode, and a Code Division Multiple Access (CDMA) method may also beused. Also, the spread spectrum demodulation section and spread spectrummodulated signal regeneration section in FIG. 19 are not limited toperforming demodulation and regeneration of a signal spread spectrummodulated with one code, and if code division multiple access is used,spread spectrum modulation and regeneration will be performed formultiplexed codes.

A specific position in the I-Q plane has been assumed for pilot symbols,as shown in FIG. 17, but this is not a limitation.

If the spreading code of a multiplexed spread spectrum signal is notknown, a receiving apparatus of a radio communication system accordingto this embodiment cannot demodulate an information modulated signal.Thus, secure radio communication can be performed by making a spreadingcode an encryption key. Information on a spreading code changed by atransmitting apparatus is a receiving apparatus encryption key.

A spread spectrum communication method is more error resistant than amodulation method in which an information signal is digitally modulated.Thus, if data of a high level of importance is transmitted using aspread spectrum system, highly reliable radio communication can beperformed. Taking this point into consideration, control informationsuch as channel information and information signal modulation methodinformation should be transmitted using a spread spectrum system.

As described above, according to this embodiment, by multiplexing aninformation modulated signal and spread modulated signal in the samefrequency band on the transmitting side, on the receiving side themultiplexed signal can be separated into an information modulated signaland spread modulated signal and demodulated, enabling the datatransmission speed to be improved by transmitting information in amultiplexed signal.

Embodiment 4

In Embodiment 4 a case is described in which an information modulatedsignal and specific modulated signal are multiplexed in the samefrequency band, and information is transmitted by the type of aparticular multiplexed specific digitally modulated signal (hereinafterreferred to as “specific signal”), and on the receiving side themultiplexed signal is separated into an information modulated signal andspecific signal.

FIG. 21 shows sample frame configurations on the time axis of a radiocommunication system according to this embodiment. FIG. 21 (A) isidentical to FIG. 16 (A), and therefore a detailed description thereofis omitted here. FIG. 21 (B) shows the frame configuration of a specificmodulated signal. Reference code 2001 and reference code 2002 indicate10-symbol specific digitally modulated symbol fields, and data symbolsand specific digitally modulated symbols are multiplexed on the timeaxis. A multiplexed specific information signal may be, for example, anyof four types—specific signal A, specific signal B, specific signal C,or specific signal D—with predetermined information contained in therespective signals. On the receiving side, information is obtained bydifferentiating between these four types of signal.

FIG. 22 shows the configuration of a transmitting apparatus 2100according to this embodiment. Parts in FIG. 22 common to those in FIG.18 are assigned the same codes as in FIG. 18, and detailed descriptionsthereof are omitted.

In FIG. 22, a specific modulated signal selection section 2101 selects aspecific signal from specific signal A, specific signal B, specificsignal C, or specific signal D corresponding to input information signalinformation, and outputs a specific signal to addition section 1703 inaccordance with the frame configuration shown in FIG. 21 (B).

Addition section 1703 adds the information modulated signal output byinformation modulation section 1701 and the specific signal output byspecific modulated signal selection section 2101, and outputs the signalresulting from the addition (multiplex signal) to band-limiting filtersection 1704.

FIG. 23 shows the configuration of a receiving apparatus 2200 accordingto this embodiment. Parts in FIG. 23 common to those in FIG. 19 areassigned the same codes as in FIG. 19, and detailed descriptions thereofare omitted. Demodulation of 16QAM modulated data symbols 1504 andspecific digitally modulated symbols 2001 in the frame configurationsshown in FIG. 21 is described below.

In FIG. 23, a specific modulated signal estimation section 2201identifies a digital signal contained in specific digitally modulatedsymbols in FIG. 21 based on an input received signal. That is to say,specific modulated signal estimation section 2201 identifies which offour signal types—specific signal A, specific signal B, specific signalC; or specific signal D—has been multiplexed. By this means, themultiplex signal is estimated and the obtained received digital signalis output to a specific modulated signal regeneration section 2203. Adistortion estimation section 2202 detects pilot symbol 1501 and pilotsymbol 1502 in FIG. 21, for example, from the received signal, andoutputs a distortion estimation signal for data symbols 1504 andspecific digitally modulated symbols 2001 to information demodulationsection 1808 and specific modulated signal regeneration section 2203.

Specific modulated signal regeneration section 2203 has as input thereceived digital signal obtained by multiplex signal estimation outputfrom specific modulated signal estimation section 2201 and atransmission path distortion signal output from distortion estimationsection 2202, estimates the multiplex signal component contained in thereceived signal, and outputs an estimated multiplex signal tosubtraction section 1807.

Delay section 1806 delays the received signal by the amount of timenecessary to generate an estimated multiplex signal, and outputs thedelayed received signal to subtraction section 1807. Subtraction section1807 subtracts the estimated multiplex signal output from specificmodulated signal regeneration section 2203 from the delayed receivedsignal output from delay section 1806, and outputs a received signalfrom which the multiplex signal component has been removed toinformation demodulation section 1808.

By means of a receiving apparatus with the above-describedconfiguration, a specific signal multiplexed with an informationmodulated signal can be identified, and the data transmission speed isimproved in proportion to the information transmitted by the multiplexedspecific signal.

In the case shown in FIG. 22, the pilot signal generation function hasbeen described as being assigned to information modulation section 1701,but this function may also be assigned to specific modulated signalselection section 2101. Also, as a different method, an apparatusconfiguration is possible in which a pilot signal generation section isprovided, and the pilot signal generation function is not assigned toinformation modulation section 1701 or specific modulated signalselection section 2101.

The frame configurations are not limited to those shown in FIG. 21, and,for example, pilot symbols need not be inserted. In this case, a pilotsignal generation function is not necessary. Also, a unique word,preamble, or other control symbols may be inserted.

In the receiving apparatus in FIG. 23, time synchronization with thetransmitting apparatus is possible by computing the correlation betweena multiplex signal and specific signal, for example, and detecting powerpeaks. This is the same as detecting a specific signal component of amultiplex signal.

The configurations of a transmitting apparatus and receiving apparatusare not limited to the configurations shown in FIG. 22 and FIG. 23.

In FIG. 22, use of a single-carrier method is described for aninformation modulated signal, but the method is not limited to asingle-carrier method, and a multicarrier method such as an OrthogonalFrequency Division Multiplex (OFDM) method may be used. In this case,the horizontal axis in FIG. 21 showing frame configurations may beconsidered to be the frequency axis. Also, a case has been described inwhich 16QAM modulation is used as the modulation method, but BPSKmodulation, QPSK modulation, or the like may also be used.

If a specific signal is not known, a receiving apparatus of a radiocommunication system according to this embodiment cannot demodulate aninformation modulated signal. Thus, secure radio communication can beperformed by making the specific signal correspondence method anencryption key. In a transmitting apparatus, information that changesthe correspondence method in a selection section that selects a specificsignal corresponding to an information signal from among a plurality ofspecific signals is a receiving apparatus encryption key.

Information transmitted by selecting a specific signal is more errorresistant than a modulation method in which an information signal isdigitally modulated. Thus, if data given correspondence to a specificsignal is data of a high level of importance, highly reliable radiocommunication can be performed. Taking this point into consideration,control information such as channel information and information signalmodulation method information should be transmitted given correspondenceto a specific signal.

As described above, according to this embodiment, the data transmissionspeed can be improved by multiplexing an information modulated signaland a particular specific signal in the same frequency band andtransmitting information with a type of particular specific signal thatis multiplexed, and separating the multiplexed signal into aninformation modulated signal and specific signal on the receiving side.

Embodiment 5

In Embodiment 5, a radio communication method, base station apparatus,and communication terminal apparatus are described in which a modulationmethod whereby information is digitally modulated is used forshort-range communications.

FIG. 24 shows the locations of a base station apparatus andcommunication terminal apparatuses according to this embodiment. Asystem is here assumed to comprise a base station apparatus 2301,communication terminal apparatus 2302, communication terminal apparatus2303, and communication terminal apparatus 2304. It is here assumed thatbase station apparatus 2301 transmits the multiplex signals described inEmbodiment 3 and Embodiment 4.

In a radio communication system according to Embodiment 3 or Embodiment4, a feature of the modulation method for digital modulating informationis that the data transmission speed is high but the area in whichreception is possible is small. Also, a feature of spread spectrumcommunication and particular specific digitally modulated signals isthat the data transmission speed is low but the area in which receptionis possible is large.

At this time, for example, the limit of the area in which a signal inwhich information is modulated by a modulation method wherebyinformation is digitally modulated according to Embodiment 3 orEmbodiment 4 can be received is indicated by reference code 2305, andthe limit of the area in which a modulated signal modulated by a spreadspectrum communication method of a radio communication system accordingto Embodiment 3 or a specific digital modulation method of a radiocommunication system according to Embodiment 4 can be received isindicated by reference code 2306.

With the modulation method whereby information is digitally modulated ina radio communication system according to Embodiment 3 or Embodiment 4,information A for high-speed data transmission is provided, and with thespread spectrum communication method of a radio communication systemaccording to Embodiment 3 or a specific digital modulation method of aradio communication system according to Embodiment 4, information B forlow-speed data transmission is provided. Thus, different kinds ofinformation—such as information A for high-speed data transmission andinformation B for low-speed data transmission—can be provided at thesame frequency, and the reception ranges of different kinds ofinformation differ.

In this case, it is assumed that, for example, communication terminalapparatus 2302 is a dedicated communication terminal apparatus that canreceive information B for low-speed transmission from a spread spectrumcommunication method of a radio communication system according toEmbodiment 3 and a specific digital modulation method of a radiocommunication system according to Embodiment 4. It is assumed thatcommunication terminal apparatus 2303 is a dedicated communicationterminal apparatus that can receive information A for high-speedtransmission from a modulation method whereby information is digitallymodulated in a radio communication system according to Embodiment 3 orEmbodiment 4.

It is assumed that communication terminal apparatus 2304 is acommunication terminal apparatus that can receive information B forlow-speed transmission from a spread spectrum communication method of aradio communication system according to Embodiment 3 and a specificdigital modulation method of a radio communication system according toEmbodiment 4, and can receive information A for high-speed transmissionfrom a modulation method whereby information is digitally modulated in aradio communication system according to Embodiment 3 or Embodiment 4.Then, when communication terminal apparatus 2304 is within area 2305,both information A and information B can be received, and communicationterminal apparatus 2304 receives either or both of information A and/orinformation B, and when communication terminal apparatus 2304 is outsidearea 2305 and within area 2306, communication terminal apparatus 2304receives information B.

Thus, according to this embodiment, by using a radio communicationsystem characterized by the use of a modulation method wherebyinformation is digitally modulated for short-range communications, it ispossible to perform transmission and reception of different kinds ofinformation in the same frequency band.

Embodiment 6

In this embodiment, a description is given of a transmitting apparatusthat multiplexes and transmits a digitally modulated first modulatedsignal and spread spectrum modulated second modulated signal in the samefrequency band of the same time, and places signal points of the firstmodulated signal and second modulated signal at different positions inthe in-phase-quadrature plane, and a receiving apparatus that receivesand demodulates this multiplex signal.

A transmitting apparatus and receiving apparatus of this embodiment havealmost the same configurations as transmitting apparatus 1700 andreceiving apparatus 1800 of above-described Embodiment 3. Therefore, inthis embodiment, the configuration of the transmitting apparatus andreceiving apparatus will be described using FIG. 18 and FIG. 19 onceagain. The only parts that differ between a transmitting apparatus ofthis embodiment and transmitting apparatus 1700 of Embodiment 3 areinformation modulation section 1701 and spread spectrum modulationsection 1702, and therefore information modulation section 1701 andspread spectrum modulation section 1702 will be described below.

A transmitting apparatus of this embodiment performs modulationprocessing so that signal points are arranged at different positions inthe in-phase-quadrature plane (I-Q plane) by information modulationsection 1701 and spread spectrum modulation section 1702 in FIG. 18.That is to say, modulation processing is performed by informationmodulation section 1701 and spread spectrum modulation section 1702 sothat the I-Q plane signal points of an information modulated signalobtained by information modulation section 1701 and the I-Q plane signalpoints of a spread modulated signal obtained by spread spectrummodulation section 1702 are different.

By this means, the correlation between a transmitted informationmodulated signal and spread spectrum modulated signal can be lowered ina transmitting apparatus of this embodiment, enabling the error rate tobe reduced when the respective modulated signals are demodulated on thereceiving side.

Examples of signal point arrangements are shown in FIG. 25 and FIG. 26.FIG. 25 shows an example of the signal point arrangement when QPSKmodulation processing is performed by information signal modulationsection 1701 and spread spectrum modulation section 1702. By performingn/4 shift QPSK modulation processing, information signal modulationsection 1701 forms an information modulated signal with the signal pointarrangement shown by the black and white circles in the figure. On theother hand, spread spectrum modulation section 1702 forms a spreadspectrum modulated signal with the signal point arrangement shown by thewhite circles in the figure.

A case has been described here in which the signal point arrangement isswitched alternately between the black circles and white circles in thefigure by having information signal modulation section 1701 perform n/4shift QPSK modulation processing, but the signal point arrangement mayalso be fixed at the positions shown by the black circles in the figureby performing QPSK modulation and shifting the signal point phase byn/4.

FIG. 26 shows an example of the signal point arrangement when BPSKmodulation processing is performed by information signal modulationsection 1701 and spread spectrum modulation section 1702. By performingn/2 shift BPSK modulation processing, information signal modulationsection 1701 forms an information modulated signal with the signal pointarrangement shown by the white and black circles in the figure. On theother hand, spread spectrum modulation section 1702 forms a spreadspectrum modulated signal with the signal point arrangement shown by theblack circles in the figure.

A case has been described here in which the signal point arrangement isswitched alternately between the white circles and black circles in thefigure by having information signal modulation section 1701 perform n/2shift BPSK modulation processing, but the signal point arrangement mayalso be fixed at the positions shown by the white circles in the figureby performing BPSK modulation and shifting the signal point phase byn/4.

The difference between receiving apparatus 1800 in FIG. 19 described inEmbodiment 3 and a receiving apparatus of this embodiment is that spreadspectrum demodulation section 1803 and information demodulation section1808 demodulate signals arranged at different signal points.

The configuration of the spread spectrum demodulation section is shownin FIG. 27. In spread spectrum demodulation section 2600, a receivedsignal in which an information modulated signal and spread spectrummodulated signal are multiplexed is input to a despreading section 2603and synchronization section 2601. Synchronization section 2601, whichcomprises matched filters, forms a synchronous timing signal based on acorrelation value between the spread spectrum part in the receivedsignal and a spreading code, and sends this synchronous timing signal toa code generation section 2602. Code generation section 2602 generates aspreading code at timing in accordance with the synchronous timingsignal, and sends this spreading code to despreading section 2603.

Despreading section 2603 performs despreading processing by multiplyingthe input received multiplex signal by the spreading code. By thismeans, only the signal prior to spread spectrum processing is restoredby despreading from within the received multiplex signal. That is tosay, there is only a noise component with a very low signal level due todespreading processing, and as a result, this is eliminated bydespreading section 2603.

At this time, signal points of an information modulated signal andspread spectrum modulated signal are arranged differently in the I-Qplane, and the correlation value is kept low, so that no noise componentdue to the information modulated signal is output from despreadingsection 2603, and only the signal prior to spread spectrum processing isoutput. The despread signal is demodulated by a demodulation section2604, whereby the signal prior to spreading modulation is restored.

The restored signal is sent to spread spectrum modulated signalregeneration section 1805 in FIG. 19. Spread spectrum modulated signalregeneration section 1805 again executes the same kind of modulationprocessing as in transmitting-side spread spectrum modulation section1702 (FIG. 18) on the input signal. At this time, spread spectrummodulated signal regeneration section 1805 executes spread spectrummodulation processing taking account of the distortion estimation signaloutput from distortion estimation section 1804. By this means, a spreadspectrum modulated signal containing transmission path distortion isregenerated, and this signal is sent to subtraction section 1807.

Subtraction section 1807 subtracts the signal regenerated by spreadspectrum modulated signal regeneration section 1805 from the receivedmultiplex signal, and consequently outputs Only an information modulatedsignal. Information demodulation section 1808 demodulates theinformation signal taking account of transmission path distortion of theinformation modulated signal input from subtraction section 1807 basedon the distortion estimation signal input from distortion estimationsection 1804.

As a result, an information signal on which digital modulationprocessing was executed and an information signal on which spreadspectrum modulation processing was executed are both restored.

Thus, according to the above configuration, when a first transmit signalis digitally modulated, a second transmit signal is spread spectrummodulated, and these signals are multiplexed and transmitted in the samefrequency band, by arranging the signal points of the respectivemodulated signals at different positions in the I-Q plane, in additionto obtaining an improvement in transmission speed it is also possible tolower the correlation between the spread spectrum modulated signal andfirst digitally modulated signal, thereby enabling communication qualityto be improved.

The present invention is not limited to a case where a signal in whichinformation is digitally modulated and a spread spectrum modulatedsignal are transmitted by a single carrier, and multicarriertransmission, as exemplified by OFDM, may also be used. An example oftransmission using both OFDM and OFDM-spreading modulation is describedin an embodiment later herein.

In this embodiment, a case has been described in which the spreadspectrum modulation communication system code multiplexing number isone, but a multiplicity—that is to say, CDMA as the spread spectrumcommunication method—may also be used. In this way, the number ofmultiplexed data can be greatly increased, enabling the datatransmission speed to be significantly improved.

Embodiment 7

In this embodiment, a description is given of a transmitting apparatusthat multiplexes in the same frequency band of the same time andtransmits a digitally modulated first modulated signal, a plurality ofspread spectrum modulated signals that have undergone spread spectrumprocessing using different spreading codes, and spreading codeinformation, and a receiving apparatus that receives and demodulatesthis multiplex signal.

In FIG. 28, in which parts corresponding to those in FIG. 18 areassigned the same codes as in FIG. 18, reference code 2700 indicates theoverall configuration of a transmitting apparatus according toEmbodiment 7. In transmitting apparatus 2700, an information signal isinput to a selection section 2701. Selection section 2701 has as input aselection control signal from a system control unit (not shown), andselectively outputs an information signal to information modulationsection 1701, or a spread spectrum modulation section 2702 that usesspreading code X or a spread spectrum modulation section 2703 that usesspreading code Y in a spread spectrum modulation section 2705, inaccordance with that selection control signal.

Information modulation section 1701 executes QPSK modulation processing,for example, on the input signal, and sends the processed signal toaddition section 1703. Spread spectrum modulation sections 2702 and 2703external spread spectrum processing on the input signal using spreadingcodes X and Y respectively, and send the processed signal to additionsection 1703.

The selection control signal is also input to a multiplexing informationmodulation section 2704. Multiplexing information modulation section2704 modulates selection control signal information—that is, multiplexframe information—and sends the modulated signal to addition section1703.

That is to say, in multiplexing information modulation section 2704,information is modulated that indicates which part of the informationsignal is modulated by information modulation section 1701, which partis modulated by spread spectrum modulation section 2702, and which partis processed by spread spectrum modulation section 2703.

Addition section 1703 adds the modulated signals input from modulationsections 1701 and 2702 through 2704, thereby multiplexing these signals.FIG. 29 shows an example of a multiplex signal output from additionsection 1703. In this embodiment, as shown in FIG. 29 (A), pilot symbols(P) are placed before and after data symbols modulated by informationmodulation section 1701, and multiplexing information symbols modulatedby multiplexing information modulation section 2704 are placed inlocations bounded by the pilot symbols.

Also, as shown in FIG. 29 (B), symbols that have been spread spectrummodulated by spread spectrum modulation section 2702 using spreadingcode X are multiplexed in the same frequency band as particular datasymbols. Furthermore, as shown in FIG. 29 (C), symbols that have beenspread spectrum modulated by spread spectrum modulation section 2703using spreading code Y are multiplexed in the same frequency band asparticular data symbols.

As a result, in transmitting apparatus 2700, three or more signals canbe multiplexed and transmitted in the same frequency band of the sametime, as shown in FIG. 29, thereby enabling significantly faster datatransmission to be performed than in the case of above-describedEmbodiments 1 through 6.

FIG. 30 shows the configuration of a receiving apparatus 2900 thatreceives and demodulates a multiplex transmit signal transmitted bytransmitting apparatus 2700. A multiplex transmit signal received by anantenna 2901 undergoes-predetermined radio reception processing by aradio section 2902, and is then sent to a delay section 2903, spreadingcode X spread spectrum demodulation section 2904, spreading code Yspread spectrum demodulation section 2905, and multiplexing informationdemodulation section 2906.

Spread spectrum demodulation section 2904 performs despreadingprocessing on the input multiplex signal using spreading code X. By thismeans, only the original signal spread on the transmitting side usingspreading code X is output. This signal is output as an informationsignal, and is also sent to a spread spectrum modulated signalregeneration section 2907.

Spread spectrum modulated signal regeneration section 2907 performsspreading processing on the input signal using spreading code X. By thismeans, the same kind of spread spectrum modulated signal as the spreadspectrum modulated signal output from spread spectrum modulation section2702 (FIG. 28) is regenerated from spread spectrum modulated signalregeneration section 2907, and this is sent to a subtraction section2909.

Similarly, spread spectrum demodulation section 2905 performsdespreading processing on the input multiplex signal using spreadingcode Y. By this means, only the original signal spread on thetransmitting side using spreading code Y is output. This signal isoutput as an information signal, and is also sent to a spread spectrummodulated signal regeneration section 2908.

Spread spectrum modulated signal regeneration section 2908 performsspreading processing on the input signal using spreading code Y. By thismeans, the same kind of spread spectrum modulated signal as the spreadspectrum modulated signal output from spread spectrum modulation section2703 (FIG. 28) is regenerated from spread spectrum modulated signalregeneration section 2908, and this is sent to subtraction section 2909.

Multiplexing information demodulation sect ion 2906 demodulates themultiplexing information symbols contained in the received multiplexsignal. Here, as can be seen from FIG. 29, multiplexing informationsymbols are not multiplexed with other signals, and are positioned in aregular fashion close to pilot symbols, making it possible formultiplexing information symbols to be demodulated easily and accuratelyby multiplexing information demodulation section 2906. The demodulatedmultiplexing information is then sent to subtraction section 2909 and adata selector 2910.

Subtraction section 2909 subtracts the regenerated signal that hasundergone spread spectrum processing with spreading code X and theregenerated signal that has undergone spread spectrum processing withspreading code Y from the received multiplex signal input with timingadjusted by delay section 2903. At this time, subtraction section 2909performs subtraction processing while controlling as appropriate thetype and timing of the regenerated spread spectrum modulated signal tobe subtracted from the received multiplex signal based on themultiplexing information.

That is to say, as shown in FIG. 29, there are cases where only a signalspread spectrum modulated by means of spreading code X is multiplexedwith respect to data symbols to be extracted by subtraction section 2909in the received multiplex signal, and cases where a signal spreadspectrum modulated by means of spreading code X and two signals spreadspectrum modulated by means of spreading code Y are multiplexed, andtherefore subtraction section 2909 reads these different kinds ofinformation from the multiplexing information, and extracts only thedata symbols in FIG. 29 (A).

An information demodulation section 2911 demodulates a pre-modulationinformation signal by executing demodulation processing (in the case ofthis embodiment, QPSK demodulation processing) corresponding toinformation modulation section 1701 of transmitting apparatus 2700 ondata symbols input from subtraction section 2909.

Demodulated data demodulated by information demodulation section 2911,spread spectrum demodulation section 2904, and spread spectrumdemodulation section 2905, is input to data selector 2910. Multiplexinginformation demodulated by multiplexing information demodulation section2906 is also input to data selector 2910. Data selector 2910 selectivelyoutputs the respective demodulated data based on the multiplexinginformation. By this means, the original signal prior to division byselection section 2701 of transmitting apparatus 2700 is output fromdata selector 2910.

Thus, according to the above configuration, by performing spreadingprocessing using a plurality of spreading codes on signals multiplexedin the same frequency band, the number of signals that can bemultiplexed can be increased, enabling significantly faster datatransmission to be performed.

In the above-described embodiment, a case has been described in whichmultiplexing information symbols are transmitted in the same frame asdata symbols, as shown in FIG. 29, but the present invention is notlimited to this, and multiplexing information symbols may also betransmitted multiplexed with data symbols as shown in FIG. 31. By sodoing it is possible to greatly increase the amount of data that can betransmitted in the same frequency band, enabling significantly fasterdata transmission to be performed.

The configuration of a transmitting apparatus in this case will now bedescribed, using FIG. 28 once again. Multiplexing information modulationsection 2704 in FIG. 28 executes spread spectrum modulation processingon multiplexing information, using a different spreading code (Z) fromspreading codes X and Y. Then it is only necessary for addition to beperformed by addition section 1703 so that spread multiplexinginformation symbols are multiplexed in the same frequency band togetherwith data symbols obtained by information modulation section 1701,spread symbols obtained by spread spectrum modulation section 2702, andspread symbols obtained by spread spectrum modulation section 2703, asshown in FIG. 31. By this means, multiplexing information can beseparated on the receiving side easily and with very little degradationdue to multiplexing.

FIG. 32 shows the configuration of a receiving apparatus that receivesand demodulates a multiplex transmit signal in which spreading codeinformation symbols have undergone spread spectrum modulation processingand multiplexing.

In FIG. 32, in which parts corresponding to those in FIG. 30 areassigned the same codes as in FIG. 30, receiving apparatus 3100 sends areceived multiplex signal output from radio section 2902 to a spreadmultiplexing information demodulation section 3101.

Spread multiplexing information demodulation section 3101 executesdespreading processing on the received multiplex signal using spreadingcode Z. By this means, only multiplexing information is output fromspread multiplexing information demodulation section 3101, and thatmultiplexing information is sent to a spread spectrum modulated signalregeneration section 3102, subtraction section 3103, and data selector2910.

Spread spectrum modulated signal regeneration section 3102 again spreadsthe multiplexing information by spreading the multiplexing informationusing spreading code Z, and sends the signal resulting from spreadingprocessing to subtraction section 3103.

Subtraction section 3103 extracts only an information signal bysubtracting the signals regenerated by spread spectrum modulated signalregeneration section 2907, spread spectrum modulated signal regenerationsection 2908, and spread spectrum modulated signal regeneration section3102 from the received multiplex signal input from delay section 2903based on timing indicated by the multiplexing information, and sendsthis information signal to information demodulation section 2911.

Data selector 2910 selectively outputs the input demodulated signalssequentially, with multiplexing information as a select signal. Thus,the original signal prior to separation and multiplexing on thetransmitting side is output from data selector 2910.

In this embodiment a case has been described in which multiplexinginformation is transmitted together with a plurality of spread spectrummodulated signals, but the present invention is not limited to this, andit is also possible for spreading code information (spreading codes Xand Y) to by transmitted together with a plurality of spread spectruminformation instead of multiplexing information or in addition tomultiplexing information.

The present invention is not limited to a case where a signal in whichinformation is digitally modulated and a spread spectrum modulatedsignal are transmitted by a single carrier, and multicarriertransmission, as exemplified by OFDM, may also be used.

In this embodiment, a case has been described in which the spreadspectrum modulation communication system code multiplexing number is twoor three, but the number may be four or more. In this way, the number ofmultiplexed data can be greatly increased, enabling the datatransmission speed to be significantly improved.

Embodiment 8

In this embodiment, a description is given of a transmitting apparatusthat comprises a first modulation section that performs digitalmodulation of an information signal and obtains a first modulatedsignal, a second modulation section that forms a plurality of specificmodulated signals modulated in a specific known arrangement decidedbeforehand together with the receiving side, a selection section thatselects a specific modulated signal corresponding to the informationsignal from among the plurality of specific modulated signals, amultiplexing section that multiplexes the first modulated signal and thespecific modulated signal selected by the selection section in the samefrequency band and obtains a multiplex signal, and a transmissionsection that transmits the multiplex signal, wherein the first andsecond modulation sections perform modulation processing so that thesignal points of the first modulated signal and specific modulatedsignal are arranged at different positions in the in-phase-quadratureplane; and a description is given of a corresponding receivingapparatus.

A transmitting apparatus and receiving apparatus of this embodiment havealmost the same configurations as transmitting apparatus 2100 andreceiving apparatus 2200 of above-described Embodiment 4. Therefore,FIG. 22 and FIG. 23 will be used again in the description of thisembodiment.

The difference between a transmitting apparatus of this embodiment andtransmitting apparatus 2100 of Embodiment 4 is that, in a transmittingapparatus of this embodiment, information modulation section 1701 andspecific modulated signal selection section 2101 perform modulationprocessing so that the respective signal points are arranged indifferent positions in the I-Q plane.

That is to say, modulation processing is performed by informationmodulation section 1701 and specific modulated signal selection section2101 so that the I-Q plane signal points of an information modulatedsignal obtained by information modulation section 1701 and the I-Q planesignal points of a specific modulated signal obtained by specificmodulated signal selection section 2101 are different.

By this means, the correlation between a transmitted informationmodulated signal and specific modulated signal can be lowered in atransmitting apparatus of this embodiment, enabling the error rate to bereduced when the respective modulated signals are demodulated on thereceiving side.

Specific modulated signal selection section 2101 is actually configuredas shown in FIG. 33. In specific modulated signal selection section 3200of this embodiment, an information signal is input to a plurality ofspecific signal generation sections 3201 through 3204 and a selectionsection 3205. Specific signal generation sections 3201 through 3204generate modulated signals with different signal arrangements accordingto the input information signal.

For example, when a “00” information signal is input, specific signal Ageneration section 3201 generates a first specific modulated signal witha first signal arrangement, and when a “01” information signal is input,specific signal B generation section 3202 generates a second specificmodulated signal with a second signal arrangement different from thefirst signal arrangement. Similarly, when a “10” information signal isinput, specific signal C generation section 3203 generates a thirdspecific modulated signal with a third signal arrangement different fromthe first and second signal arrangements, and when a “11” informationsignal is input, specific signal D generation section 3204 generates afourth specific modulated signal with a fourth signal arrangementdifferent from the first through third signal arrangements.

One of these specific modulated signals is then selected and output byselection section 3205. That is to say, selection section 3205 outputs afirst specific modulated signal when “00” is input as an informationsignal, outputs a second specific modulated signal when “01” is input,outputs a third specific modulated signal when “10” is input, andoutputs a fourth specific modulated signal when “11” is input.

Then, as described above, data symbols and specific modulation symbolsare multiplexed and transmitted from transmitting apparatus 2100 (FIG.22) as shown in FIG. 21. This specific modulated signal can easily byseparated from an information signal by the receiving apparatus that isthe communicating party, but cannot be separated by a receivingapparatus other than the communicating party, and constitutes aninterference signal, enabling an information signal to be givensecurity.

That is to say, by providing specific modulated signal estimationsection 2201 of receiving apparatus 2200 shown in FIG. 23 with acorrelator corresponding to each signal arrangement generated byspecific signal generation sections 3201 through 3204 (FIG. 33), it ismade possible for specific modulated signal estimation section 2201 tooutput only the specific signal generated by each of specific signalgeneration sections 3201 through 3204 from within a received multiplexsignal.

Then by outputting this specific signal directly as an informationsignal, it is possible to use this information signal as significantinformation. Also, if the specific signal estimated by specificmodulated signal estimation section 2201 is regenerated as the samespecific modulated signal as at the time of transmission by specificmodulated signal regeneration section 2203, and then sent to subtractionsection 1807, it is possible for the specific modulated signal to beeliminated from the received multiplex signal by subtraction section1807, and for only the information modulated signal to be extracted.

In contrast to this, a receiving apparatus other than communicatingparty receiving apparatus 2200 does not know the signal arrangement ofthe specific signal, and therefore cannot separate the specific signalfrom the received multiplex signal, and cannot extract the informationsignal.

In addition, in a transmitting apparatus of this embodiment, informationmodulated signal I-Q plane signal points and specific modulated signalI-Q plane signal points are made to differ, and therefore thecorrelation between an information modulated signal and specificmodulated signal is lowered, and the error rate can be reduced whenmodulated signals are demodulated on the receiving side. In fact, theprecision of correlation computation by specific modulated signalestimation section 2201 shown in FIG. 23 improves, and each specificsignal can be faithfully restored.

A description will be given here using FIG. 25 and FIG. 26. FIG. 25shows an example of a case in which QPSK modulation processing isperformed by information signal modulation section 1701 (FIG. 22) andspecific signal generation sections 3201 through 3204 in specificmodulated signal selection section 2101 (FIG. 33). By performing n/4shift QPSK modulation processing, information signal modulation section1701 forms an information modulated signal with the signal pointarrangement shown by the black and white circles. On the other hand,specific signal generation sections 3201 through 3204 form specificmodulated signals with the signal point arrangement shown by the whitecircles.

FIG. 26 shows an example of a case in which BPSK modulation processingis performed by information signal modulation section 1701 and specificsignal generation sections 3201 through 3204. By performing n/2 shiftBPSK modulation processing, information signal modulation section 1701forms an information modulated signal with the signal point arrangementshown by the white and black circles. On the other hand, specific signalgeneration sections 3201 through 3204 form specific modulated signalswith the signal point arrangement shown by the black circles.

Thus, according to the above configuration, when a digitally modulatedinformation signal and a specific modulated signal modulated using aspecific arrangement also known beforehand by the receiving side aremultiplexed and transmitted in the same frequency band, by performingmodulation processing so that signal point positions in the I-Q planediffer between the information modulated signal and specific modulatedsignal, it is possible to perform high-speed transmission of data thathas security, and also to suppress degradation of communication qualitydue to multiplexing.

This embodiment, also, is not limited to a case where a signal in whichinformation is digitally modulated and a spread spectrum modulatedsignal are transmitted by a single carrier, and multicarriertransmission, as exemplified by OFDM, may also be used.

The transmitting apparatus and receiving apparatus configurations arenot limited to the configurations in FIG. 22 and FIG. 23, and can beimplemented with modifications as appropriate.

Embodiment 9

In this embodiment there are proposed a transmitting apparatus thatmultiplexes in the same frequency band and transmits an OFDM modulatedsignal and an OFDM-spreading modulation modulated signal, and areceiving apparatus that receives and demodulates that multiplextransmit signal.

FIG. 34 shows sample frame configurations on the frequency-time axesaccording to this embodiment. In FIG. 34, one block indicated by fineshading represents one OFDM modulated symbol, one block indicated bycoarse shading represents one OFDM-spreading modulation modulated chip,and one block indicated by diagonal hatching represents one pilot signalsymbol.

As can be seen from FIG. 34, a transmitting apparatus of this embodimentmultiplexes and transmits an OFDM modulated signal and OFDM-spreadingmodulation modulated signal in the same frequency band of the same time.By this means, extremely high-speed data transmission is possible bymultiplexing an OFDM-spreading modulation modulated signal in additionto an OFDM modulated signal for which high-speed data transmission ispossible by itself.

In this embodiment, OFDM modulation processing is performed for a pilotsignal, but unlike data symbols, multiplexing is not performed at thesame frequency of the same time with OFDM-spreading modulation. As aresult, pilot symbols can be extracted easily during reception anddemodulation.

That is to say, with OFDM modulation, subcarriers are modulated so as tohave a mutually orthogonal relationship, and therefore, when the pilotsymbols shown in FIG. 34 are viewed at the same time, pilot symbols ofdifferent frequencies can easily be restored without degradation bydemodulating each subcarrier. Then, if the same kind of processing isperformed at a different point in time, another pilot symbol can also berestored.

A transmitting apparatus of this embodiment is configured as shown inFIG. 35. Transmitting apparatus 3400 performs serial/parallel conversionprocessing on a first information signal by means of a serial/parallelconversion section (S/P) 3401, and then sends the resulting signal to anaddition section 3404.

Also, transmitting apparatus 3400 executes spreading processing on asecond information signal by means of a spreading section 3402, executesserial/parallel conversion processing by means of a serial/parallelconversion section (S/P) 3403, and then sends the resulting signal toaddition section 3404.

After these two signals are added by addition section 3404, theresulting signal undergoes inverse discrete Fourier transform processingby an inverse discrete Fourier transform section (idft) 3405. By thismeans, a multiplex transmit signal is formed in which an OFDM modulatedsignal and OFDM-spreading modulated signal with the frame configurationsshown in FIG. 34 are multiplexed in the same frequency band.

This multiplex transmit signal is subjected to predetermined radioprocessing by a radio section 3406, is amplified by an amplificationsection 3407, and transmitted from an antenna 3408. Thus, alarge-capacity multiplex transmit signal in which an OFDM modulatedsignal and OFDM-spreading modulated signal are multiplexed in the samefrequency band is transmitted from transmitting apparatus 3400.

A receiving apparatus of this embodiment is configured as shown in FIG.36. On receiving a multiplex transmit signal in which an OFDM modulatedsignal and OFDM-spreading modulated signal are multiplexed in the samefrequency band at antenna 3501, receiving apparatus 3500 performspredetermined reception processing in a radio section 3502. The signalthat has undergone radio reception processing is subjected to discreteFourier transform processing by a discrete Fourier transform section(dft) 3503, and the processed signal is sent to a delay section 3509,parallel/serial conversion section (P/S) 3504, and distortion estimationsection 3508.

The received multiplex signal that has undergone parallel/serialconversion by parallel/serial conversion section 3504 is input to adespreading section 3505, where despreading processing is executed. Thesignal output from despreading section 3505 is only a signal that wassubject to OFDM-spreading modulation; an OFDM signal becomes a noisecomponent with a very low signal level through despreading, and isconsequently eliminated by despreading section 3505. The output ofdespreading section 3505 is sent to a demodulation section 3506.

Demodulation section 3506 executes demodulation processing correspondingto primary modulation executed on the transmitting side. In transmittingapparatus 3400 shown in FIG. 35 the configuration of the primarymodulation section corresponding to this demodulation section 3506 isomitted, but in fact, modulation sections that execute modulationprocessing corresponding to an information demodulation section 3511described later herein and demodulation section 3506 are provided on theinput side of serial/parallel conversion section 3401 and on the inputside of spreading section 3402.

The signal prior to OFDM-spreading modulation demodulated bydemodulation section 3506 is output directly as a second informationsignal, and is also sent to a regeneration section 3507. Transmissiondistortion information estimated by distortion estimation section 3508is also input to regeneration section 3507. Distortion estimationsection 3508 estimates transmission distortion based on the pilot signalcontained in the received multiplex signal.

Regeneration section 3507 regenerates an OFDM-spreading modulated signalby executing on the second information signal obtained by demodulationsection 3506 the same spreading processing and serial/parallelconversion processing as performed on the transmitting side, and sendsthis signal to a subtraction section 3510.

A received multiplex signal delayed by delay section 3509 by an amountequivalent to the processing delay of parallel/serial conversion section3504, despreading section 3505, demodulation section 3506, andregeneration section 3507 is input to subtraction section 3510. Bysubtracting the OFDM-spreading modulated signal from the receivedmultiplex signal, subtraction section 3510 outputs only an OFDMmodulated signal. Information demodulation section 3511 restores thefirst information signal by executing demodulation processingcorresponding to the transmitting-side primary modulation processing onthe OFDM modulated signal, and outputs this restored signal.

In this embodiment, the positions of signal points of an OFDM modulatedsignal and the positions of signal points of an OFDM-spreading modulatedsignal are arranged so as to be mutually different. By this means, evenwhen an OFDM modulated signal and OFDM-spreading modulated signal aremultiplexed in the same frequency band, interference between the signalscan be obviated, and moreover the correlation between the signals can belowered, enabling data errors to be suppressed during demodulation. Infact, since the correlation between an OFDM-spreading modulated signaland OFDM modulated signal is low, it is possible for only anOFDM-spreading modulated signal to be extracted by despreading section3505.

Examples of signal point arrangements are shown in FIG. 25 and FIG. 26.FIG. 25 shows an example of a case in which an OFDM modulated signal andOFDM-spreading modulated signal are QPSK modulated. Through n/4 shiftQPSK modulation, an OFDM modulated signal has the signal pointarrangement shown by the black and white circles. On the other hand,through QPSK modulation, an OFDM-spreading modulated signal has thesignal point arrangement shown by the white circles.

FIG. 26 shows an example of a case in which an OFDM modulated signal andOFDM-spreading modulated signal are BPSK modulated. Through n/2 shiftBPSK modulation, an OFDM modulated signal has the signal pointarrangement shown by the white and black circles. On the other hand,through BPSK modulation, an OFDM-spreading modulated signal has thesignal point arrangement shown by the black circles.

Thus, according to the above configuration, by multiplexing andtransmitting an OFDM modulated signal and OFDM-spreading modulatedsignal in the same frequency band, it is possible to perform extremelyhigh-speed data transmission.

Also, by making the signal point positions in the I-Q plane differentfor an OFDM modulated signal and an OFDM-spreading modulated signal, itis possible to suppress signal degradation due to multiplexing, and thetwo signals can be separated with few data errors.

In this embodiment a case has been described in which, as described withregard to FIG. 35, when an OFDM-spreading modulated signal is formed,spreading processing is performed by spreading section 3402, and thenserial/parallel conversion processing is performed by serial/parallelconversion section 3403. That is to say, mutually orthogonal subcarriersare formed after an information signal is spread on the frequency axis.

However, the present invention is not limited to this, and it is alsopossible for spreading processing to be performed after serial/parallelconversion processing is performed, as in the case of transmittingapparatus 3600 shown in FIG. 37. That is to say, it is also possible tofirst assign an information signal to a plurality of mutually orthogonalsubcarriers, and then perform spreading processing on asubcarrier-by-subcarrier basis.

In this case, as shown in FIG. 38, in the configuration of a receivingapparatus 3700 it is only necessary to reverse the order of connectionof despreading section 3505 and parallel/serial conversion section 3504,and perform parallel/serial conversion processing after despreadingprocessing.

Embodiment 10

In this embodiment an OFDM modulated signal and OFDM-spreading modulatedsignal are multiplexed and transmitted in the same frequency band, andspreading code information used when performing OFDM-spreadingmodulation processing is also transmitted.

By this means, it is possible not only to transmit large amounts of databut also to perform highly secure communication between a transmittingapparatus and receiving apparatus of this embodiment. That is to say, ifspreading code information is used as an encryption key only betweenmutually communicating parties, it is possible to share spreading codeinformation with only a specific communicating party.

As a result, another communication terminal is unable to restore anOFDM-spreading modulated signal. Moreover, the inability to restore anOFDM-spreading modulated signal also means an inability to isolate andrestore an OFDM modulated signal multiplexed at the same frequency andat the same time.

For example, rules can be decided beforehand between mutuallycommunicating parties to the effect that “00” spreading code informationcorresponds to spreading code A, “01” spreading code informationcorresponds to spreading code B, “10” spreading code informationcorresponds to spreading code C, and “11” spreading code informationcorresponds to spreading code D.

FIG. 39 and FIG. 40 show sample frame configurations of a multiplextransmit signal when transmitting spreading code information (multiplexspreading code information symbols). FIG. 39 shows frame configurationsin the case where multiplex spreading code information symbols aretransmitted by subcarriers of different frequencies at the same time,and FIG. 40 shows frame configurations in the case where multiplexspreading code information symbols are transmitted in the same frequencyband.

As is clear from FIG. 39 and FIG. 40. multiplex spreading codeinformation symbols are arranged so as not to be multiplexed with othersymbols or chips in respect of at least one of the elements of time orfrequency. For example, in FIG. 39, multiplex spreading code informationsymbols are multiplexed with OFDM symbols, OFDM-spreading modulationsymbols, and pilot symbols in the frequency direction, but areindependent in the time direction. In FIG. 40, on the other hand,multiplex spreading code information symbols are multiplexed with OFDMsymbols, OFDM-spreading modulation symbols, and pilot symbols in thetime direction, but are independent in the frequency direction.

This enables multiplex spreading code information symbols to beextracted easily on the receiving side.

FIG. 41, in which parts corresponding to those in FIG. 35 are assignedthe same codes as in FIG. 35, shows the configuration of a transmittingapparatus 4000 of this embodiment. Transmitting apparatus 4000 forms amultiplex transmit signal with the frame configuration shown in FIG. 39.Transmitting apparatus 4000 executes serial/parallel conversionprocessing by means of a serial/parallel conversion section (S/P) 4001on spreading code information output from the system control unit (notshown) of transmitting apparatus 4000, and then sends the resultingsignal to an addition section 4002.

Addition section 4002 adds a first information signal that has undergoneserial/parallel conversion by serial/parallel conversion section 3401, asecond information signal that has undergone spreading processing andserial/parallel conversion processing by a spreading section 3402 andserial/parallel conversion section 3403, and spreading code informationthat has undergone serial/parallel conversion by serial/parallelconversion section 4001. The signal resulting from this addition is thensubjected to inverse discrete Fourier transform processing by an inversediscrete Fourier transform section (idft) 4003.

Thus in transmitting apparatus 4000, by performing serial/parallelconversion on spreading code information, followed by addition andinverse discrete Fourier transform processing, spreading codeinformation is superimposed on a plurality of subcarriers in a mutuallyorthogonal relationship together with an OFDM modulated signal andOFDM-spreading modulated signal, as shown in FIG. 39.

FIG. 42, in which parts corresponding to those in FIG. 38 are assignedthe same codes as in FIG. 38, shows the configuration of a receivingapparatus 4100 that receives and demodulates a multiplex transmit signaltransmitted from transmitting apparatus 4000 in FIG. 41. In receivingapparatus 4100, a received multiplex signal that has undergone discreteFourier transform processing is input to a spreading code informationdemodulation section 4101. Spreading code information demodulationsection 4101 extracts only spreading code information from the receivedmultiplex signal, and demodulates this spreading code information.

As shown in FIG. 39, spreading code information of this embodiment ismultiplexed with OFDM symbols, OFDM-spreading modulation symbols, andpilot symbols in the frequency direction, but is independent in the timedirection, enabling spreading code information to be extracted easily byspreading code information demodulation section 4101 by coordinatingtiming with the spreading code information.

Spreading code information demodulation section 4101 demodulates thespreading code information extracted in this way, selects a spreadingcode specification signal corresponding to the demodulated data fromamong held spreading code specification signals based on rules knownonly to transmitting apparatus 4000 and receiving apparatus 4100, andsends this spreading code specification signal to despreading section3505 and a regeneration section 4102.

By this means, despreading section 3505 can restore the secondinformation signal prior to OFDM-spreading modulation processing byperforming despreading processing using the spreading code specified bythe spreading code specification signal. Other receiving apparatuses, onthe other hand, cannot restore the OFDM-spreading modulated signal asthey do not know the spreading code.

Regeneration section 4102 regenerates an OFDM-spreading modulated signalby executing the same spreading processing and serial/parallelconversion processing as performed on the transmitting side on thesecond information signal obtained by despreading section 3505, usingthe spreading code corresponding to the spreading code specificationsignal.

Thus, according to the above configuration, an OFDM modulated signal andOFDM-spreading modulated signal are multiplexed in the same frequencyband, and also information on a spreading code used when performingOFDM-spreading modulation processing is transmitted as encryption keyinformation that can be known only to a specific communicating party, asa result of which it is possible not only to perform high-speed datatransmission but also to perform highly secure communication.

In the above embodiment, a description has been given of theconfigurations of a transmitting apparatus 4000 that forms a multiplextransmit signal in which spreading code information is arranged in thesame time direction, as shown in FIG. 39, and a receiving apparatus 4100that receives and demodulates that multiplex transmit signal, but atransmitting apparatus that forms a transmit signal in which spreadingcode information is arranged in the same frequency direction, as shownin FIG. 40, may also be configured as shown in FIG. 43.

In FIG. 43, in which parts corresponding to those in FIG. 41 areassigned the same codes as in FIG. 41, in communication apparatus 4200spreading code information is input directly to an addition section 4201without undergoing serial/parallel conversion processing. An inversediscrete Fourier transform section 4202 executes inverse discreteFourier transform processing so that spreading code information isassigned to the same frequency. By this means, a multiplex transmitsignal with the frame configuration shown in FIG. 40 is formed.

In this case, a receiving apparatus can have almost the sameconfiguration as receiving apparatus 4100 shown in FIG. 42. Spreadingcode information can then easily be extracted by having information of apredetermined frequency extracted by spreading code informationdemodulation section 4101.

In this embodiment, also, a case has been described in which, whenforming an OFDM-spreading modulated signal, spreading processing isperformed by spreading section 3402, followed by serial/parallelconversion processing by serial/parallel conversion section 3403, butthe present invention is not limited to this, and it is also possiblefor spreading processing to be performed after serial/parallelconversion processing, as described in Embodiment 9. In this case, it isonly necessary for the receiving apparatus to perform parallel/serialconversion processing after despreading processing accordingly.

Embodiment 11

In this embodiment a method is proposed whereby, firstly, as shown inFIG. 44 (A), an OFDM modulated signal and OFDM-spreading modulatedsignal are multiplexed and transmitted at specific times, and at timesother than the specific times, either an OFDM modulated signal or anOFDM-spreading modulated signal is transmitted.

Also, secondly, as shown in FIG. 44 (B), an OFDM modulated signal andOFDM-spreading modulated signal are multiplexed and transmitted onspecific subcarriers, and on subcarriers other than the specificsubcarriers, either an OFDM modulated signal or an OFDM-spreadingmodulated signal is transmitted.

By this means, in this embodiment it is possible to perform high-speedtransmission of large amounts of data.

The configuration of a transmitting apparatus of this embodiment isshown in FIG. 45. In transmitting apparatus 4400, a first informationsignal is input to an OFDM-spreading modulation parallel signalgeneration section 4401, and a second information signal is input to anOFDM and OFDM-spreading modulation multiplex parallel signal generationsection 4402.

OFDM spreading modulation parallel signal generation section 4401 iscomposed of a spreading section and a parallel/serial conversionsection, and generates spreading-processed parallel signals from thefirst information signal.

OFDM and OFDM-spreading modulation multiplex parallel signal generationsection 4402 has the kind of configuration shown in the initial stage ofFIG. 37. That is to say, a serial/parallel conversion section, and aserial/parallel conversion section and spreading section, are connectedin parallel to the input stage of an addition section, a serial/parallelconverted parallel signal and spread serial/parallel converted parallelsignal are input to the addition section, and these two parallel signalsare added by the addition section.

The parallel signal generated by OFDM-spreading modulation parallelsignal generation section 4401 and the spread parallel signal generatedby OFDM and OFDM-spreading modulation multiplex parallel signalgeneration section 4402 are subjected to inverse discrete Fouriertransform processing by an inverse discrete Fourier transform section(idft) 4403, to become a multiplex transmit signal with a frameconfiguration as shown in FIG. 44.

A multiplex transmit signal that has undergone inverse discrete Fouriertransform processing is transmitted via a radio section 4404, amplifier4405, and antenna 4406. A multiplex transmit signal transmitted in thisway is received and demodulated by a receiving apparatus 4500 with theconfiguration shown in FIG. 46.

In receiving apparatus 4500, a signal received by an antenna 4501 isinput to a discrete Fourier transform section (dft) 4503 via a radiosection 4502. The received multiplex signal that has undergone discreteFourier transform processing by discrete Fourier transform section 4503is sent to an OFDM-spreading modulation demodulating section 4504 thatperforms the reverse of the processing of OFDM-spreading modulationparallel signal generation section 4401 (FIG. 45), and is also sent toan OFDM and OFDM-spreading modulation multiplex signal demodulatingsection 4505 that performs the reverse of the processing of OFDM andOFDM-spreading modulation multiplex parallel signal generation section4402 (FIG. 45).

Then only the first information signal prior to OFDM-spreadingmodulation is demodulated by OFDM-spreading modulation demodulatingsection 4504. Also, the multiplexed OFDM modulated signal andOFDM-spreading modulated signal are each demodulated by OFDM andOFDM-spreading modulation multiplex signal demodulating section 4505.

Thus, according to the above configuration, by providing a region inwhich an OFDM modulated signal and OFDM-spreading modulated signal aremultiplexed and transmitted, and a region in which only an OFDMmodulated signal or OFDM-spreading modulated signal is transmitted, itis possible not only to perform high-speed transmission of large amountsof data but also to perform communication with greater diversity.

A case has been described in which, in transmitting apparatus 4400 inFIG. 45, an OFDM-spreading modulation parallel signal is generated byOFDM-spreading modulation parallel signal generation section 4401, andan OFDM-spreading modulated signal is assigned to other than specifictimes or specific subcarriers in which an OFDM modulated signal andOFDM-spreading modulated signal are multiplexed, but the presentinvention is not limited to this, and if an OFDM parallel signalgeneration section is used instead of OFDM-spreading modulation parallelsignal generation section 4401, it is possible for an OFDM modulatedsignal to be assigned to other than specific times or specificsubcarriers.

Embodiment 12

In this embodiment, spread spectrum symbols are multiplexed andtransmitted together with data symbols in the same frequency band of thesame time. Then information is placed on spread spectrum symbols, andspread spectrum symbols are used on the receiving side as a signal forsynchronization.

By this means, in this embodiment high-speed data transmission can beperformed and receiving-side synchronization processing can be performedaccurately and easily.

FIG. 48 shows the configuration of a transmitting apparatus 4700 of thisembodiment. In FIG. 48, in which parts corresponding to those in FIG. 6are assigned the same codes as in FIG. 6, transmitting apparatus 4700 isequipped with a spread spectrum modulation section 4701 instead ofdigital modulation section 502.

Spread spectrum modulation section 4701 has as input a secondinformation signal different from the first information signal input toinformation modulation section 501, and forms a spread spectrum signalby performing spreading processing using a predetermined spreading code.The digitally modulated signal obtained by information modulationsection 501 and spread spectrum signal obtained by spread spectrummodulation section 4701 are added by addition section 503. Theprocessing subsequent to addition section 503 is similar to theprocessing described with regard to FIG. 6, and therefore a descriptionthereof is omitted here.

FIG. 49 shows the configuration of a receiving apparatus 4800 of thisembodiment. In FIG. 49, in which parts corresponding to those in FIG. 19are assigned the same codes as in FIG. 19, receiving apparatus 4800 hasa similar configuration to receiving apparatus 1800 in FIG. 19, exceptfor having a synchronization section 4801.

Synchronization section 4801 has as input a received multiplex signalwith the frame configuration shown in FIG. 47. Synchronization section4801 multiplies the received multiplex signal by the same spreading codeas used by spread spectrum modulation section 4701 of transmittingapparatus 4700 (FIG. 48).

By this means, in synchronization section 4801 a correlation value peakis detected at the point in time at which a spread spectrum symbolwithin the received multiplex signal is input. Taking the point in timeat which this peak is detected as synchronization timing,synchronization section 4801 sends a synchronization timing signal tospread spectrum demodulation section 1803, spread spectrum modulatedsignal regeneration section 1805, distortion estimation section 1804,and information demodulation section 1808.

Spread spectrum demodulation section 1803 extracts only spread spectrumsymbols from the received multiplex signal by multiplying the receivedmultiplex signal by the same spreading code as used by spread spectrummodulation section 4701 (FIG. 48), at the synchronization timing signaltiming. Spread spectrum symbols demodulated by this means are output asa second information signal, and are also sent to spread spectrummodulated signal regeneration section 1805.

Spread spectrum modulated signal regeneration section 1805 regenerates aspread spectrum modulated signal by multiplying the demodulated spreadspectrum symbols by a spreading code at timing based on thesynchronization signal timing signal. In subtraction section 1807, aframe containing data symbols shown in the upper part of FIG. 50 isextracted by subtracting the regenerated spread spectrum modulatedsignal from the received multiplex signal.

Based on the synchronization timing signal from synchronization section4801, information demodulation section 1808 demodulates the input signalat timing delayed by the delay section 1806 delay time and subtractionsection 1807 processing time with respect to that synchronization timingsignal. By this means, the first information signal is demodulated.

Incidentally, in this embodiment, the pilot symbols (P) located oneither side of data symbols in a frame containing data symbols are usedas a signal for estimating transmission path distortion.

Thus, according to the above configuration, by multiplexing andtransmitting a digitally modulated first information signal and a spreadspectrum modulated Second information signal in the same frequency bandof the same time, it becomes unnecessary to insert a signal for firstinformation signal synchronization in the same frame as the firstinformation signal. The fact that a synchronization signal is notnecessary allows information signal insertion in first informationsignal frames to be increased accordingly, enabling high-speedtransmission to be performed.

Also, significantly faster data transmission is made possible by notonly transmitting a spread spectrum modulated signal for synchronizationbut also transmitting second information.

In the above embodiment, a case has been described in which spreadspectrum symbols are multiplexed as a signal for synchronization, but itis also possible for known symbols to be multiplexed and transmittedinstead of spread spectrum symbols, as shown in FIG. 50.

In this case, also, it is unnecessary to insert synchronization symbolsin frames containing data symbols, enabling a greater amount of data tobe included in those frames, and making possible high-speed datatransmission.

In this case, a transmitting apparatus may be configured as shown inFIG. 51. The difference between transmitting apparatus 5000 in FIG. 51,in which parts corresponding to those in FIG. 48 are assigned the samecodes as in FIG. 48, and transmitting apparatus 4700, is thattransmitting apparatus 5000 is equipped with a known signal generationsection 5001 instead of spread spectrum modulation section 4701.

A receiving apparatus for this case may be configured as shown in FIG.52. Differences between receiving apparatus 5100 in FIG. 52, in whichparts corresponding to those in FIG. 49 are assigned the same codes asin FIG. 49, and receiving apparatus 4800, are that a synchronizationsection 5102 detects synchronization timing based on computation ofcorrelation with a known symbol contained in a received multiplexsignal, and also that a known signal regeneration section 5101regenerates a known signal at the synchronization timing detected bysynchronization section 5102 and with a distortion component estimatedby distortion estimation section 1804 added.

Synchronization section 5102 holds a symbol that is the same as a knownsymbol, and calculates a correlation value between this held symbol andthe received multiplex signal at all times. When a maximum correlationvalue is detected at a point in time at which a known symbol is input,synchronization section 5102 takes that timing as synchronizationtiming.

Embodiment 13

In this embodiment there are proposed a transmission method wherebymodulated signals of spread spectrum communication systems withdifferent spreading ratios are multiplexed, and a transmitting apparatusand receiving apparatus that use that transmission method.

FIG. 53 shows transmit signal frame configurations formed when thetransmission method of this embodiment is used. With spread spectrumcommunication system A, following control symbols, each symbol is spreadwith spread spectrum system A that has a predetermined spreading ratiobefore being transmitted. As described later herein, control symbols areused to perform time synchronization between transmission and reception,estimation of transmission path distortion, or estimation andelimination of frequency offset on the receiving apparatus side, and aretransmitted without being multiplexed with a spread spectrumcommunication system A modulated signal or spread spectrum communicationsystem B modulated signal.

With spread spectrum communication system B, on the other hand, eachsymbol is spread with a different spreading ratio from spread spectrumsystem A (twice the spreading ratio in the case of this embodiment)before being transmitted. The signals formed by these spread spectrumsystems A and B comprising different spreading ratios are thenmultiplexed in the same frequency band and transmitted. Here, as thespread spectrum system B spreading ratio is twice that of spreadspectrum system A, one spread spectrum communication system B symbol ismultiplexed for two spread spectrum communication system A symbols.

In this embodiment, one symbol is spread over four chips by spreadspectrum system A as shown in FIG. 54, and one symbol is spread overeight chips by spread spectrum system B as shown in FIG. 55. Also, inspread spectrum systems A and B, spread modulated signals for aplurality of channels (channels 1 and 2) are formed by using spreadingcodes with a correlation-value of almost 0.

The configuration of a transmitting apparatus that multiplexes andtransmits spread modulated signals with different spreading ratios inthis way is shown in FIG. 56. In transmitting apparatus 5500, a firsttransmit digital signal D1 is input to a spread spectrum communicationsystem A modulation section 5501, and a second transmit digital signalD2 is input to a spread spectrum communication system B modulationsection 5502. In addition, a frame configuration signal S1, comprisingframe information for forming frames such as shown in FIG. 53, is inputto spread spectrum communication system A modulation section 5501 andspread spectrum communication system B modulation section 5502.

Spread spectrum communication system A modulation section 5501 forms aspread spectrum communication system A quadrature baseband signal byexecuting modulation such as QPSK or 16QAM, for example, on firsttransmit digital signal D1, and then performing spreading processing ofone symbol over four chips, as described above. On the other hand,spread spectrum communication system B modulation section 5502 forms aspread spectrum communication system B quadrature baseband signal byexecuting modulation such as QPSK or 16QAM, for example, on secondtransmit digital signal D2, and then performing spreading processing ofone symbol over eight chips.

Spread spectrum communication system A modulation section 5501 andspread spectrum communication system B modulation section 5502 send thesignals that have undergone spreading processing to an addition section5503. In spread spectrum communication system A modulation section 5501,control symbols are added at the head of a frame as shown in FIG. 53 inaccordance with frame configuration signal S1. Here, a case is describedin which control symbols are added by spread spectrum communicationsystem A modulation section 5501, but control symbols may also be addedat a predetermined position in a frame by spread spectrum communicationsystem B modulation section 5502.

Addition section 5503 multiplexes the two input modulated spread signalswith different spreading ratios, and sends the signal resulting fromthis multiplexing to a band-limiting filter 5504. A multiplex signalband-limited by band-limiting filter 5504 is subjected to predeterminedradio processing by a radio section 5505, and is then transmitted froman antenna 5507 via an amplifier 5506.

Spread spectrum communication system A modulation section 5501 andspread spectrum communication system B modulation section 5502 areconfigured as shown in FIG. 57. As spread spectrum communication systemA modulation section 5501 and spread spectrum communication system Bmodulation section 5502 have virtually identical configurations, exceptfor having different spreading ratios, the configuration of spreadspectrum communication system A modulation section 5501 will bedescribed here.

In spread spectrum communication system A modulation section 5501,transmit digital signal D1 is input to a channel 1 modulation andspreading section 5601 and channel 2 modulation and spreading section5602. Channel 1 modulation and spreading section 5601 executesmodulation such as QPSK or 16QAM, for example, on transmit digitalsignal D1, and then spreads one symbol over four chips by executingspreading processing. Similarly, channel 2 modulation and spreadingsection 5602 executes modulation such as QPSK or 16QAM, for example, ontransmit digital signal D1, and then spreads one symbol over four chipsby executing spreading processing using a spreading code with acorrelation value of almost 0 with respect to channel 1 modulation andspreading section 5601. Channel 1 modulation and spreading sections 5601and 5602 add control symbols at the head of a frame in accordance withframe configuration signal S1. The signal obtained by channel 1modulation and spreading section 5601 and the signal obtained by channel2 modulation and spreading section 5602 are multiplexed by an additionsection 5603.

Thus, a signal for a plurality of channels, code division multiplexedusing mutually orthogonal spreading codes with the same spreading ratio,is output from spread spectrum communication system A modulation section5501. Spread spectrum communication system B modulation section 5502performs almost the same kind of processing as channel 1 modulation andspreading section 5601, except for using a spreading code with twice thespreading ratio of that of channel 1 modulation and spreading section5601 and not adding control symbols, and forms a code divisionmultiplexed signal for a plurality of channels.

FIG. 58 shows the configuration of a receiving apparatus 5700 accordingto this embodiment that receives and demodulates a signal transmitted bytransmitting apparatus 5500. In receiving apparatus 5700, predeterminedradio processing is performed by a radio section 5702 on a receivedsignal received by an antenna 5701. Following radio processing, thesignal is sent to a subtraction section 5704 via a delay section 5703,and is also sent to a spread spectrum communication system Bdemodulation section 5706 and distortion estimation section 5708.

Spread spectrum communication system B demodulation section 5706 obtainsa pre-spreading digital signal by performing the reverse of theprocessing of transmitting-side spread spectrum communication system Bmodulation section 5502 on the input signal. This spread spectrumcommunication system B demodulated signal is output directly as ademodulated signal and is also sent to a spread spectrum communicationsystem B modulated signal regeneration section 5707.

Spread spectrum communication system B modulated signal regenerationsection 5707 forms a spread spectrum communication system B replicasignal by performing spreading modulation processing by means of spreadspectrum communication system B once again on the once demodulatedspread spectrum communication system B signal.

At this time, spread spectrum communication system B modulated signalregeneration section 5707 forms a replica signal that includes theamount of distortion in transmission by forming a replica signal usingtransmission path distortion information estimated by distort ionestimation section 5708 using control symbols. Spread spectrumcommunication system B modulated signal regeneration section 5707actually forms a replica signal by performing respreading on the oncedemodulated spread spectrum communication system B signal, andremodulating the signal using transmission path distortion information.Spread spectrum communication system B modulated signal regenerationsection 5707 sends the formed replica signal to subtraction section5704.

In subtraction section 5704, the spread spectrum communication system Bmodulated signal replica signal obtained by spread spectrumcommunication system B modulated signal regeneration section 5707 issubtracted from the spread spectrum communication system A modulatedsignal and spread spectrum communication system B modulated signalmultiplex signal delayed by delay section 5703 by the amount of time forforming the replica signal, by which means only the spread modulatedsignal spread and modulated by means of spread spectrum communicationsystem A is extracted.

The extracted spread spectrum communication system A spread modulatedsignal is made a pre-spreading digital signal by being demodulated by aspread spectrum communication system A demodulation section 5705.

Thus, according to receiving apparatus 5700, even when spread signalsspread using spread spectrum systems with different spreading ratios aretransmitted multiplexed in the same frequency band, these signals spreadby means of spread spectrum systems with different spreading ratios canbe separated, and individually demodulated.

Spread spectrum communication system A demodulation section 5705 andspread spectrum communication system B demodulation section 5706 may beconfigured as shown in FIG. 59, for example. Here, the case of spreadspectrum communication system A demodulation section 5705 will bedescribed. In spread spectrum communication system A demodulationsection 5705, a signal spread and modulated by spread spectrum system Aextracted by subtraction section 5704 is input to a synchronizationsection 5801, channel 1 despreading section 5803, and channel 2despreading section 5804.

Synchronization section 5801 detects despreading timing based on asynchronization signal added to the input signal, and sends the detecteddespreading timing signal to a channel 1 code generation section 5802and channel 2 code generation section 5805. Channel 1 code generationsection 58C2 and channel 2 code generation section 5805 generate aspreading code used for channel 1 and a spreading code used for channel2, respectively, at timing in accordance with the despreading timingsignal, and send these spreading codes to channel 1 despreading section5803 and channel 2 despreading section 5804. The post-despreadingsignals obtained by channel 1 despreading section 5803 and channel 2despreading section 5804 are demodulated by a channel 1 demodulationsection 5806 and channel 2 demodulation section 5807, respectively, andas a result become channel 1 and channel 2 digital signals.

In FIG. 59 a configuration is illustrated in which spread modulatedsignals for two channels are demodulated, but it goes without sayingthat the number of channels is not limited to this, and any number ofchannels can be selected. For example, FIG. 60 shows a sampleconfiguration of spread spectrum communication system A demodulationsection 5705 and spread spectrum communication system B demodulationsection 5706 when a spread modulated signal for one channel isdemodulated.

The case of spread spectrum communication system A demodulation section5705 will be described here. In spread spectrum communication system Ademodulation section 5705, a signal spread and modulated by spreadspectrum system A extracted by subtraction section 5704 is input to asynchronization section 5901 and a channel 1 despreading section 5903.

Synchronization section 5901 detects despreading timing based on asynchronization signal added to the input signal, and sends the detecteddespreading timing signal to a channel 1 code generation section 5902.Channel 1 code generation section 5902 generates a spreading code usedfor channel 1 at timing in accordance with the despreading timingsignal, and sends this spreading code to a channel 1 despreading section5903. The post-despreading signal obtained by channel 1 despreadingsection 5903 is demodulated by a channel 1 demodulation section 5904,and as a result becomes a channel 1 digital signal.

In addition to such a configuration, in the case of this embodimentspread spectrum communication system B transmission power is madegreater than spread spectrum communication system A transmission power.

Specifically, in the case illustrated by the I-Q plane in FIG. 61 (here,a case in which QPSKmodulation processing is performed will bedescribed), distance r_(B) of a spread spectrum communication system Bsignal point 6201 from the origin is greater than distance r_(A) of aspread spectrum communication system A signal point 6202 from theorigin—that is, r_(B)>r_(A). That is to say, in this embodiment, spreadspectrum communication system B transmission power relevant to replicasignal formation is made greater than spread spectrum communicationsystem A transmission power.

By this means, a spread spectrum communication system B replica signalformed by spread spectrum communication system B demodulation section5706 and spread spectrum communication system B modulated signalregeneration section 5707 can be made a much more e accurate signal.

This will now be explained in detail. In receiving apparatus 5700 inFIG. 58, the signal input to spread spectrum communication system Bdemodulation section 5706 is a received quadrature baseband signal inwhich signals modulated and spread by means of spread spectrumcommunication system A and spread spectrum communication system Brespectively are multiplexed.

Therefore, when despreading processing is performed in spread spectrumcommunication system B demodulation section 5706 using a spreading codecorresponding to spread spectrum communication system B, if thecross-correlation between the spreading code corresponding to spreadspectrum communication system B and the spreading code corresponding tospread spectrum communication system A is high, it is not possible foronly a signal spread by means of spread spectrum communication system Bto be separated with a high degree of precision.

To prevent this problem, in this embodiment spread spectrumcommunication system B signal power is made greater than spread spectrumcommunication system A signal power, thereby improving despreadingprecision by lowering the correlation between a spread spectrumcommunication system B signal and a spread spectrum communication systemA signal, and enabling spread spectrum communication system Bdemodulation section 5706 to extract only a signal spread by means ofspread spectrum system B with a high degree of precision. By this means,a highly accurate replica signal can be formed by spread spectrumcommunication system B modulated signal regeneration section 5707,enabling a signal spread by means of spread spectrum communicationsystem A also to be extracted with a high degree of precision bysubtraction section 5704.

Also, in this embodiment, when spread signals with different spreadingratios are separated from a received multiplex signal in receivingapparatus 5700, a spread spectrum communication system B signal, whichhas a large spreading ratio, is first separated by despreading. As aspread signal with a large spreading ratio has greater spreading gain,separation precision is higher for the spread signal separated first(the spread spectrum communication system B signal). As a result,replica signal precision is improved, and the separation precision ofthe spread signal with a small spreading ratio extracted next (thespread spectrum communication system A signal) is also improved.Consequently, all spread signals can be separated and demodulated withgood precision.

According to the above configuration, by transmitting modulated signalsof spread spectrum communication systems with different spreading ratiosmultiplexed in the same frequency band on the transmitting side, and onthe receiving side, forming a replica signal by despreading and thenrespreading one or other of the multiplexed signals, and separating andextracting multiplexed signals by subtracting the replica signal fromthe multiplex signal, it is possible to demodulate both multiplexedsignals. As a result, the data transmission speed can be improved.

The method described in this embodiment whereby, of the multiplexedsignals, the transmission power of a signal for which a replica signalfor subtraction is formed is made greater than the transmission power ofother multiplexed signals, is also effective when applied to otherabove-described embodiments and embodiments described later herein.

For example, a case will here be described in which this method isapplied when an information modulated signal and spread spectrumcommunication system modulated signal are multiplexed in the samefrequency band, as described in Embodiment 3. Here, signal points of aninformation modulated signal are denoted by reference numeral 6202 inFIG. 61, signal points of a spread spectrum communication systemmodulated signal by reference numeral 6201, the distance between aspread spectrum communication system signal point 6201 and the origin byr_(B), and the distance between a spread spectrum communication systemsignal point 6202 and the origin by r_(A). It is here assumed thatr_(B)>r_(A). That is to say, spread spectrum communication systemtransmission power relevant to replica signal formation is made greaterthan information modulation transmission power.

By this means, the correlation with an information signal, whichrepresents interference with respect to a spread spectrum signal, ismade small, and consequently the reception characteristics of aninformation signal obtained from spread spectrum demodulation section1803 in FIG. 19 improve. As a result, the despreading precision ofspread spectrum demodulation section 1803 can be improved, making itpossible to extract only a spread spectrum processed signal with a highdegree of precision. A highly accurate replica signal can therefore beformed by spread spectrum modulated signal regeneration section 1805,enabling an information modulated signal also to be extracted with ahigh degree of precision by the subtraction section.

In addition, the method described in this embodiment whereby, whensignals generated using spreading codes with different spreading ratiosare multiplexed in the same frequency band, signals are separated anddemodulated in order from the signal with the largest spreading ratio,also enables a similar effect to be obtained when applied to embodimentsdescribed later herein.

In this embodiment, a receiving apparatus 5700 has been described thatis provided with both a spread spectrum communication system Ademodulation section 5705 that demodulates a spread spectrumcommunication system A signal and a spread spectrum communication systemB demodulation section 5706 that demodulates a spread spectrumcommunication system B signal, as shown in FIG. 59, but it is notabsolutely essential for demodulation sections that demodulate allmultiplexed signals to be provided. For example, if only spread spectrumcommunication system A demodulation section 5705 is provided, adedicated receiving apparatus can be implemented that receives anddemodulates only a spread spectrum communication system A signal, and ifonly spread spectrum communication system B demodulation section 5706 isprovided, a dedicated receiving apparatus can be implemented thatreceives and demodulates only a spread spectrum communication system Bsignal.

In this embodiment, a case has been described in which signals of twochannels are transmitted and received in the case of both spreadspectrum communication system A and spread spectrum communication systemB, but it goes without saying that any number of channels can beselected. For example, three or more channels may be multiplexed forspread spectrum communication system A and spread spectrum communicationsystem B respectively.

In this embodiment, the description has referred to multiplexing of twosystems, spread spectrum communication system A and spread spectrumcommunication system B, but this is not a limitation, and multiplexingmay also be performed of three or more spread spectrum communicationsystems with different spreading ratios. Also, modulated signals thatare not spread at the same time—that is to say, that are not spreadspectrum communication system signals—may be multiplexed at the sametime.

Embodiment 14

In this embodiment there are proposed a transmitting apparatus thatmultiplexes in the same frequency band and transmits signals of aplurality of OFDM-spreading modulation systems formed using spreadingcodes with different spreading ratios, and a receiving apparatus thatreceives and demodulates that multiplex transmit signal. In thisembodiment so-called frequency domain spreading is performed, wherebychips spread by a spreading code are spread across subcarriers in thefrequency axis direction.

FIG. 62 shows sample frame configurations on the frequency-time axesaccording to this embodiment. In FIG. 62, one box is equivalent to onesymbol. As can be seen from the figure, one symbol is spread in thefrequency axis direction.

In this embodiment, the OFDM-spreading modulation system A signal shownin FIG. 62 (A) and the OFDM-spreading modulation system B signal shownin FIG. 62 (B) are transmitted multiplexed in the same frequency band.Comparing OFDM-spreading modulation system A shown in FIG. 62 (A) withOFDM-spreading modulation system B shown in FIG. 62 (B), theOFDM-spreading modulation system B spreading ratio is greater than theOFDM-spreading modulation system A spreading ratio. As a result, twiceas many OFDM-spreading modulation system A symbols as OFDM-spreadingmodulation system B symbols are transmitted in the same period.

In an OFDM-spreading modulation system A frame, control symbols arearranged in the time direction, and guard symbols (that is, sectionswhere no signal is located) are placed at positions corresponding tocontrol symbols in an OFDM-spreading modulation system B frame. By thismeans, control symbols, which are the basis for transmission pathestimation and synchronization processing, can be extracted easily andwith a high degree of precision on the receiving side.

The configuration of a transmitting apparatus that multiplexes andtransmits signals of a plurality of OFDM-spreading modulation systemsformed using spreading codes with different spreading ratios in this wayis shown in FIG. 63. In transmitting apparatus 6200, a first transmitdigital signal D1 is input to a spread spectrum communication system Amodulation section 6201, and a second transmit digital signal D2 isinput to a spread spectrum communication system B modulation section6202. In addition, a frame configuration signal S1, comprising frameinformation for forming frames such as shown in FIG. 62, is input tospread spectrum communication system A modulation section 6201 andspread spectrum communication system B modulation section 6202.

Spread spectrum communication system A modulation section 6201 forms aspread spectrum communication system A quadrature baseband signal byexecuting modulation such as QPSK or 16QAM, for example, on firsttransmit digital signal D1, and then performing spreading processing ofone symbol over four chips. On the other hand, spread spectrumcommunication system B modulation section 6202 forms a spread spectrumcommunication system B quadrature baseband signal by executingmodulation such as QPSK or 16QAM, for example, on second transmitdigital signal D2, and then performing spreading processing of onesymbol over eight chips. Spread spectrum communication system Amodulation section 6201 and spread spectrum communication system Bmodulation section 6202 send the signals that have undergone spreadingprocessing to an addition section 6203.

As shown in FIG. 62, in accordance with frame configuration signal S1,in spread spectrum communication system A modulation section 6201control symbols are added at a predetermined position in a frame, and inspread spectrum communication system B modulation section 6202 guardsymbols (null signals) are placed at positions corresponding to controlsymbols. Here, a case is described in which control symbols are added byspread spectrum communication system A modulation section 6201, butcontrol symbols may also be added at a predetermined position in a frameby spread spectrum communication system B modulation section 6202.

Addition section 6203 multiplexes the two input modulated spread signalswith different spreading ratios. The multiplexed signal undergoesserial/parallel conversion by a serial/parallel conversion section (S/P)6204, followed by inverse discrete Fourier transform processing by aninverse discrete Fourier transform section (idft) 6205. By this means,post-spreading chips are spread across a plurality of subcarriers in thefrequency direction, and a multiplex transmit signal is formed in whichan OFDM-spreading modulation system A signal and OFDM-spreadingmodulation system B signal with the frame configurations shown in FIG.62 are multiplexed in the same frequency band. This multiplex transmitsignal is subjected to predetermined radio processing by a radio section6206, and is then transmitted from an antenna 6208 via an amplifier6207.

FIG. 64 shows the configuration of a receiving apparatus 6300 accordingto this embodiment that receives and demodulates a signal transmitted bytransmitting apparatus 6200. In receiving apparatus 6300, predeterminedradio processing is performed by a radio section 6302 on a receivedsignal received by an antenna 6301. Following radio processing, thesignal undergoes Fourier transform processing by a discrete Fouriertransform section (dft) 6303 and parallel/serial conversion by aparallel/serial conversion section (P/S) 6304, whereby chips spread inthe frequency axis direction are restored to the original code divisionmultiplex signal.

The code division multiplex signal is sent to a subtraction section 6306via a delay section 6305, and is also sent to a spread spectrum system Bdemodulation section 6308 and distortion estimation section 6310.

Spread spectrum system B demodulation section 6308 obtains apre-spreading digital signal by performing the reverse of the processingof transmitting-side spread spectrum system B modulation section 6202 onthe input signal. This spread spectrum system B demodulated signal isoutput directly as a demodulated signal and is also sent to a spreadspectrum system B modulated signal regeneration section 6309.

Spread spectrum system B modulated signal regeneration section 6309forms a spread spectrum system B replica signal by performing spreadingmodulation processing by means of spread spectrum system B once again onthe once demodulated spread spectrum communication system B signal. Atthis time, spread spectrum system B modulated signal regenerationsection 6309 forms a replica signal that includes the amount ofdistortion in transmission by forming a replica signal usingtransmission path distortion information estimated by distortionestimation section 6310 using control symbols. Spread spectrum system Bmodulated signal regeneration section 6309 actually forms a replicasignal by performing respreading on the once demodulated spread spectrumsystem B signal, and remodulating the signal using transmission pathdistortion information. Spread spectrum system B modulated signalregeneration section 6309 sends the formed replica signal to subtractionsection 6306.

In subtraction section 6306, the spread spectrum system B modulatedsignal replica signal obtained by spread spectrum system B modulatedsignal regeneration section 6309 is subtracted from the spread spectrumsystem A modulated signal and spread spectrum system B modulated signalmultiplex signal delayed by delay section 6305 by the amount of time forforming the replica signal, by which means only the spread modulatedsignal spread and modulated by means of spread spectrum system A isextracted.

The extracted spread spectrum system A spread modulated signal is made apre-spreading digital signal by being demodulated by a spread spectrumsystem A demodulation section 6307.

Thus, according to receiving apparatus 6300, even when signals of aplurality of OFDM-spreading modulation systems formed using spreadingcodes with different spreading ratios are transmitted multiplexed in thesame frequency band, these OFDM-spreading modulation signals can beseparated and individually demodulated.

Signals of a plurality of channels may be code division multiplexedusing different spreading codes by configuring spread spectrumcommunication modulation system A modulation section 6201 and spreadspectrum communication modulation system B modulation section 6202 asshown in FIG. 57. In this case, the configurations of spread spectrumsystem A demodulation section 6307 and spread spectrum system Bdemodulation section 6308 of receiving apparatus 6300 should be madeconfigurations that enable despreading and demodulation of spreadsignals of a plurality of channels.

In addition to such a configuration, in the case of this embodiment, asin Embodiment 13, spread spectrum system B transmission power is madegreater than spread spectrum system A transmission power. By this means,when despreading processing is performed by spread spectrum system Bdemodulation section 6308 using a spreading code corresponding to spreadspectrum system B, the correlation between a spread signal correspondingto spread spectrum system B and a spread signal corresponding to spreadsignal A can be made small, enabling only a signal spread by means ofspread spectrum system B to be separated with a high degree ofprecision.

As a result, it possible to extract only a signal spread by means ofspread spectrum system B in spread spectrum system B demodulationsection 6308 with a high degree of precision, enabling a highly accuratereplica signal to be formed by spread spectrum system B modulated signalregeneration section 6309, and so making it possible for a signal spreadby means of spread spectrum system A also to be extracted with a highdegree of precision by subtraction section 6306.

Also, in this embodiment, when OFDM-spreading modulated signals withdifferent spreading ratios are separated from a received multiplexsignal in receiving apparatus 6300, an OFDM-spreading modulated signalwith a large spreading ratio is first separated by despreading. As anOFDM-spreading modulated signal with a large spreading ratio has greaterspreading gain, separation precision of the OFDM-spreading modulatedsignal separated first (the OFDM-spreading modulated signal using spreadspectrum communication system B) can be improved. As a result, replicasignal precision is improved, and the separation precision of theOFDM-spreading modulated signal with a small spreading ratio extractednext (the OFDM-spreading modulated signal using spread spectrumcommunication system A) is also improved. Consequently, allOFDM-spreading modulated signals can be separated and demodulated withgood precision.

According to the above configuration, by multiplexing and transmittingsignals of a plurality or OFDM-spreading modulation systems formed usingspreading codes with different spreading ratios on the transmittingside, and on the receiving side, forming a replica signal by despreadingand then respreading one or other of the multiplexed signals, andseparating and extracting multiplexed signals by subtracting the replicasignal from the multiplex signal, it is possible to demodulate bothmultiplexed signals. As a result, the data transmission speed can beimproved.

In this embodiment, a method has been described whereby signals ofOFDM-spreading modulation systems with different spreading ratios aremultiplexed in all frequency-time axis frames excluding control symbols,but this is not a limitation, and it is also possible, for example, formultiplexing to be performed only in some specific frequency-time axisframes. That is to say, it is possible for an independent OFDM signal oran independent OFDM-spreading modulation system signal with which asignal with a different spreading ratio is not multiplexed to be used inother frames. This also applies in the case of Embodiment 15 describedbelow.

In this embodiment, a receiving apparatus has been described that isprovided with both a spread spectrum system A demodulation section 6307that demodulates a spread spectrum system A signal and a spread spectrumsystem B demodulation section 6308 that demodulates a spread spectrumsystem B signal, as shown in FIG. 64, but it is not absolutely essentialfor demodulation sections that demodulate all multiplexed signals to beprovided. For example, if only spread spectrum system A demodulationsection 6307 is provided, a dedicated receiving apparatus can beimplemented that receives and demodulates only an OFDM-spreadingmodulation system A signal, and if only spread spectrum system Bdemodulation section 6308 is provided, a dedicated receiving apparatuscan be implemented that receives and demodulates only an OFDM-spreadingmodulation system B signal.

In this embodiment, the description has referred to multiplexing of twosystems, OFDM-spreading modulation system A and OFDM-spreadingmodulation system B, but this is not a limitation, and if; for example,three spreading codes with different spreading ratios are provided andthree OFDM-spreading modulation system signals are formed, and these aremultiplexed in the same frequency band, it will still be possible toseparate and demodulate signals transmitted by means of all theOFDM-spreading modulation systems with the above-described method. Thisalso applies in the case of Embodiment 15 described below.

Embodiment 15

In above-described Embodiment 14 there were proposed a transmittingapparatus that multiplexes in the same frequency band and transmitssignals of a plurality of OFDM-spreading modulation systems obtained byusing spreading codes with different spreading ratios and spreadingchips in the frequency axis direction, and a corresponding receivingapparatus, but in this embodiment, there are proposed a transmittingapparatus that multiplexes in the same frequency band and transmitssignals of a plurality of OFDM-spreading modulation systems obtained byusing spreading codes with different spreading ratios and spreadingchips in the time axis direction (so-called time domain spreading), anda corresponding receiving apparatus.

FIG. 65 shows sample frame configurations on the frequency-time axesaccording to this embodiment. In FIG. 66, one box is equivalent to onesymbol. As can be seen from the figure, one symbol is spread in the timeaxis direction.

In this embodiment, the OFDM-spreading modulation system A signal shownin FIG. 65 (A) and the OFDM-spreading modulation system B signal shownin FIG. 65 (B) are transmitted multiplexed in the same frequency band.Comparing OFDM-spreading modulation system A shown in FIG. 65 (A) withOFDM-spreading modulation system B signal in FIG. 65 (B), theOFDM-spreading modulation system B spreading ratio is greater than theOFDM-spreading modulation system A spreading ratio (in the case of thisembodiment, twice as large). As a result, twice as many OFDM-spreadingmodulation system A symbols as OFDM-spreading modulation system Bsymbols are transmitted in the same period.

In an OFDM-spreading modulation system A frame, control symbols arearranged in the time direction, and guard symbols are placed atpositions corresponding to control symbols in an OFDM-spreadingmodulation system B frame. By this means, control symbols, which are thebasis for transmission path estimation and synchronization processing,can be extracted easily and with a high degree of precision on thereceiving side.

The configuration of a transmitting apparatus that multiplexes andtransmits signals of a plurality of OFDM-spreading modulation systemsformed using spreading codes with different spreading ratios in this waywill now be described using FIG. 66. In transmitting apparatus 6500, afirst transmit digital signal D1 is input to a modulation section 6501,and a second transmit digital signal D2 is input to a modulation section6502. In addition, a frame configuration signal S1, comprising frameinformation for forming frames such as shown in FIG. 65, is input tomodulation section 6501 and modulation section 6502. Modulation sections6501 and 6502 execute QPSK or 16QAM modulation processing on the inputsignals, and send the resulting signals to a spreading system Aspreading section 6505 and spreading system B spreading section 6506 viaserial/parallel conversion sections (S/Ps) 6503 and 6504 respectively.

Spreading system A spreading section 6505 spreads one input parallelsignal symbol over, for example, four chips. On the other hand,spreading system B spreading section 6506 spreads one input parallelsignal symbol over, for example, eight chips. Post-spreading parallelsignals output from spreading system A spreading section 6505 andspreading system B spreading section 6506 are multiplexed by an additionsection 6509.

Also, a control symbol generated by a control symbol generation section6507 in accordance with frame configuration signal S1 is input toaddition section 6509 via a serial/parallel conversion section (S/P)6508, and this aerial/parallel converted control symbol is multiplexedtogether with the parallel signals output from spreading system Aspreading section 6505 and spreading system B spreading section 6506.The multiplexed signal undergoes inverse discrete Fourier transformprocessing by an inverse discrete Fourier transform section (idft) 6510.

By this means, post-spreading chips are spread in the time axisdirection, and a multiplex transmit signal is formed in which anOFDM-spreading modulation system A signal and OFDM-spreading modulationsystem B signal with the frame configurations shown in FIG. 65 aremultiplexed in the same frequency band. This multiplex transmit signalis subjected to predetermined radio processing by a radio section 6511,and is then transmitted from an antenna 6513 via an amplifier 6512.

FIG. 67 shows the configuration of a receiving apparatus 6600 accordingto this embodiment that receives and demodulates a signal transmitted bytransmitting apparatus 6500. In receiving apparatus 6600, predeterminedradio processing is performed by a radio section 6602 on a receivedsignal received by an antenna 6601. Following radio processing, thesignal undergoes Fourier transform processing by a discrete Fouriertransform section (dft) 6603 and is then input to a subtraction section6605 via a delay section 6604, and is also input to a spreading system Bdespreading section 6609 and parallel/serial conversion section (P/S)6613.

Spread spectrum system B despreading section 6609 performs the reverseof the processing of transmitting-side spread spectrum system Bspreading section 6506 on the input signal. After despreading the signalundergoes parallel/serial conversion processing by a parallel/serialconversion section (P/S) 6610, is demodulated by a demodulation section6611, and is then output directly as a demodulated signal and also inputto a spreading system B signal regeneration section 6612. Meanwhile, thesignal resulting from parallel/serial conversion by parallel/serialconversion section (P/S) 6613 is input to a transmission path distortionestimation section 6614. Transmission path distortion estimation section6614 estimates transmission path distortion based on control symbols,and sends estimated transmission path distortion information tospreading system B signal regeneration section 6612. As the controlsymbols have not been subjected to spreading processing, they can beused by transmission path distortion estimation section 6614 withoutundergoing despreading processing.

Spread spectrum system B signal regeneration section 6612 performsmodulation processing again on the once demodulated spread spectrumsystem B signal, followed by serial/parallel conversion processing andspreading system B spreading processing, thereby forming a spreadspectrum system B replica signal. At this time, spreading system Bsignal regeneration section 6612 forms a replica signal that includesthe amount of distortion in transmission by forming a replica signalusing transmission path distortion information from transmission pathdistortion estimation section 6614. Spreading system B signalregeneration section 6612 sends the formed replica signal to subtractionsection 6605.

In subtraction section 6605, the spread spectrum system B replica signalobtained by spreading system B signal regeneration section 6612 issubtracted from the spread spectrum system A signal and spread spectrumsystem B signal multiplex signal delayed by delay section 6604 by theamount of time for forming the replica signal, by which means only thespread modulated signal spread and modulated by means of spread spectrumsystem A is extracted.

The extracted spread spectrum system A spread modulated signal is made apost-despreading parallel signal by undergoing despreading processing bya spreading system A despreading section 6606 using the same spreadingcode as spreading system A spreading section 6505. This parallel signalis input to a demodulation section 6608 via a parallel/serial conversionsection (P/S) 6607, and is made a demodulated signal by demodulationsection 6608.

Thus, according to receiving apparatus 6600, even when signals of aplurality of OFDM-spreading modulation systems formed by time axisspreading using spreading codes with different spreading ratios aretransmitted multiplexed in the same frequency band, these OFDM-spreadingmodulation signals can be separated and individually demodulated.

If OFDM-spreading modulation system A or OFDM-spreading modulationsystem B signals multiplexed here are configured with a plurality ofchannels, the amount of transmission information can be greatlyincreased. This can be done, for example, by configuring modulationsection 6501, serial/parallel conversion section (S/P) 6503, andspreading system A spreading section 6505 shown in FIG. 66, which forman OFDM-spreading modulation system A signal, as shown in FIG. 68. Asthis also applies to modulation section 6502, serial/parallel conversionsection (S/P) 6504, and spreading system B spreading section 6506, whichform an OFDM-spreading modulation system B signal, the case in which anOFDM-spreading modulation system A signal is formed will be describedbelow.

In FIG. 68, a first transmit digital signal D1 is sent to an additionsection 6707 via a plurality (being equal to the number of channels: inFIG. 68, two channels) of channel modulation sections 6701 and 6702,serial/parallel conversion sections (S/Ps) 6703 and 6704, and channelspreading sections 6705 and 6706. In channel 1 spreading section 6705and channel 2 spreading section 6706, spreading processing is performedusing spreading codes that have the same spreading ratio and for whichthere is almost no cross-correlation. The code division multiplexedsignal for a plurality of channels obtained by multiplexing by additionsection 6707 is sent to addition section 6509 in FIG. 66.

To demodulate OFDM-spreading modulation system A or OFDM-spreadingmodulation system B signals configured with a plurality of channels inthis way, spreading system A despreading section 6606, parallel/serialconversion section (P/S) 6607, and demodulation section 6608 shown inFIG. 67 can be configured as shown in FIG. 69. As this also applies tospreading system B despreading section 6609, parallel/serial conversionsection (P/S) 6610, and demodulation section 6611, which demodulate anOFDM-spreading modulation system B signal, a case in whichOFDM-spreading modulation system A signals of two channels aredemodulated will be described below.

In FIG. 69, an output signal from subtraction section 6605 is input to achannel 1 despreading section 6802 and channel 2 despreading section6803. Channel 1 despreading section 6802 and channel 2 despreadingsection 6803 perform despreading processing using spreading codes inputfrom a channel 1 code generation section 6801 and channel 2 codegeneration section 6804 respectively. The despread signal obtained bychannel 1 despreading section 6802 is made a channel 1 received digitalsignal by means of a parallel/serial conversion section (P/S) 6805 andchannel 1 demodulation section 6807. Similarly, the despread signalobtained by channel 2 despreading section 6803 is made a channel 2received digital signal by means of a parallel/serial conversion section(P/S) 6806 and channel 2 demodulation section 6808.

According to the above configuration, by multiplexing and transmittingsignals of a plurality of OFDM-spreading modulation systems that haveundergone time domain spreading using spreading codes with differentspreading ratios on the transmitting side, and on the receiving side,forming a replica signal by despreading and then respreading one orother of the multiplexed signals, and separating and extractingmultiplexed signals by subtracting the replica signal from the multiplexsignal, it is possible to demodulate both multiplexed signals. As aresult, the data transmission speed can be improved.

Embodiment 16

In this embodiment it is proposed that, in addition to transmitting anOFDM modulated signal and OFDM-spreading modulated signal multiplexed inthe same frequency band, selection be made of executing OFDM modulationprocessing or executing OFDM-spreading modulation processing on aninformation signal directed to each transmission target stationaccording to the radio wave propagation path environment between thetransmitting side and each transmission target station. By this means,it is possible to achieve both an improvement in error ratecharacteristics and an increase in the amount of transmit data.

FIG. 70 is a conceptual diagram of this embodiment. In FIG. 70, a basestation transmits an OFDM modulated signal and OFDM-spreading modulatedsignal multiplexed in the same frequency band to terminals A through E.For terminals in area AR1 close to the base station in terms ofdistance, an information signal subjected to OFDM modulation processingis transmitted, placing the emphasis on the amount of transmissioninformation rather than resistance to error. On the other hand, forterminals in outer area AR2 surrounding AR1, an information signal istransmitted that has undergone OFDM-spreading modulation processing,which has good error rate resistance.

To give a specific example, when one terminal E is present in area AR1,as shown in FIG. 70 (A), an information signal for terminal E is OFDMmodulated and information signals for terminals A through D areOFDM-spreading modulated, and these modulated signals are transmittedmultiplexed in the same frequency band. On the other hand, whenterminals C and D move into area AR1, as shown in FIG. 70 (B),information signals for terminals C, D, and E are OFDM modulated andinformation signals for terminals A and B are OFDM-spreading modulated,and these modulated signals are transmitted multiplexed in the samefrequency band.

FIG. 71 and FIG. 72 show sample frame configurations of a transmitsignal transmitted from the base station. FIG. 71 (A) and FIG. 72 (A)show transmit signal frame configurations when terminals A through E areat the locations shown in FIG. 70 (A), and FIG. 71 (B) and FIG. 72 (B)show transmit signal frame configurations when terminals A through Ehave moved to the locations shown in FIG. 70 (B). Reference codes Athrough E in FIG. 71 and FIG. 72 indicate signals directed to terminalsA through E respectively.

Here, OFDM-spreading modulated signals (OFDM-CDM symbols) may be spreadin the frequency axis direction, may be spread in the time axisdirection, or may be spread two-dimensionally in the frequency axisdirection and time axis direction. For OFDM symbols, when there are aplurality of terminals, OFDM signals for each terminal may be timedivision multiplexed as shown in FIG. 71 (B), or a plurality of carriersmay be used and assigned to individual terminals as shown in FIG. 72(B).

In order to simplify the explanation, in FIG. 70, FIG. 71, and FIG. 72 acase has been described in which signals that have undergone OFDMmodulation processing, which offers a large transmission volume, aretransmitted to terminals near a base station, and signals that haveundergone OFDM-spreading modulation processing, which offers goodresistance to errors, are transmitted to terminals far from the basestation, but in actuality, modulation processing is selected accordingto the radio wave propagation environment, as described below.

FIG. 73 shows the configuration of a base station of this embodiment. Inthe base station, an information signal for each terminal is input to anOFDM parallel signal generation section 7201 and OFDM spreadingmodulation parallel signal generation section 7202. OFDM parallel signalgeneration section 7201 and OFDM spreading modulation parallel signalgeneration section 7202 processes information signals of correspondingterminals in accordance with a frame configuration signal generated by aframe configuration signal generation section 7203 as a modulationselection means. For example, in the situation shown in FIG. 70 (A),OFDM parallel signal generation section 7201 processes only aninformation signal for terminal E, and OFDM spreading modulationparallel signal generation section 7202 processes information signalsfor terminals A through D.

Signals generated by OFDM parallel signal generation section 7201 andOFDM spreading modulation parallel signal generation section 7202 areadded by an addition section 7209, followed by inverse discrete Fouriertransform processing by an inverse discrete Fourier transform section(idft) 7205. By this means, information signals for the respectiveterminals for which OFDM modulation processing or OFDM-spreadingmodulation processing has been selected according to the radio wavepropagation environment are multiplexed in the same frequency band. Thesignal resulting from inverse Fourier transform processing istransmitted from an antenna 7208 via a radio section 7206 and amplifier7207.

In the receiving system, on the other hand, a signal from a terminalreceived by antenna 7208 is input to a demodulation section 7210 via aradio section 7209. Receive data demodulated by demodulation section7210 is input to a system decision section 7211. The receive data hasthe kind of frame configuration shown in FIG. 75, and based on requestinformation and radio wave propagation environment estimationinformation from each terminal, system decision section 7211 decideswhether or not to transmit an information signal to each terminal and,if an information signal is to be sent, decides whether to send an OFDMmodulated signal or OFDM-spreading modulated signal System decisionsection 7211 sends the result of the decision to frame configurationsignal generation section 7203.

The configuration of a terminal is shown in FIG. 74. In a terminal,predetermined radio processing is performed by a radio section 7302 on areceived signal received by an antenna 7301. Following radio processing,the signal undergoes Fourier transform processing by a discrete Fouriertransform section (dft) 7303, and is then input to a subtraction section7305 via a delay section on 7304, and is also input to an OFDM-spreadingsystem demodulation section 7307, transmission path distortionestimation section 7308, and radio wave propagation environmentestimation section 7309.

OFDM-spreading system demodulation section 7307 demodulates anOFDM-spreading modulated signal by performing despreading processing anddiscrete Fourier transform processing on the received multiplex signal.The demodulated OFDM-spreading modulated signal is output directly as ademodulated signal and is also input to an OFDM-spreading system signalregeneration section 7310.

In OFDM-spreading system signal regeneration section 7310, anOFDM-spreading modulated signal replica signal is formed by againexecuting modulation processing, serial/parallel conversion processing,and spreading processing on the once demodulated OFDM-spreadingmodulated signal. At this time, OFDM-spreading system signalregeneration section 7310 forms a replica signal that includes theamount of distortion in transmission by forming a replica signal usingtransmission path distortion information from transmission pathdistortion estimation section 7308. OFDM-spreading system signalregeneration section 7310 sends the formed replica signal to subtractionsection 7305.

In subtraction section 7305, the OFDM-spreading modulated signal replicasignal obtained by OFDM-spreading system signal regeneration section7310 is subtracted from the received multiplex signal delayed by delaysection 7304 by the amount of time for forming the replica signal, bywhich means only an OFDM modulated signal is extracted. The extractedOFDM modulated signal is demodulated by an OFDM system demodulationsection 7306.

Radio wave propagation environment estimation section 7309 estimates theradio wave propagation environment, such as the SIR (Signal toInterference Ratio), Doppler frequency, received field strength, ormultipath environment, and sends the estimation result to a transmitframe generation section 7311. In addition to the radio wave propagationenvironment estimation result, transmit data D1 and request informationD2 requesting signal transmission are also input to transmit framegeneration section 7311. Using these signals, transmit frame generationsection 7311 generates the kind of transmit frame shown in FIG. 75. Theoutput from transmit frame generation section 7311 is transmitted fromantenna 7301 via an quadrature baseband signal generation section 7312,radio section 7313, and amplifier 7314.

Thus, according to the above configuration, an OFDM-spreading modulatedsignal that is resistant to errors is transmitted to a transmissiontarget station for which the propagation environment is poor, and anOFDM modulated signal with a high transmission rate is transmitted to atransmission target station for which the propagation environment isgood, these signals being transmitted multiplexed in the same frequencyband, thereby making it possible to achieve both an improvement in errorrate characteristics and an increase in the amount of transmit data.

In this embodiment, a case has been described in which execution of OFDMmodulation processing or execution of OFDM-spreading modulationprocessing is selected for an information signal directed to a terminalaccording to the radio wave propagation environment, but it is alsopossible to execute both OFDM modulation processing and OFDM-spreadingmodulation processing on the information signal of each terminal andtransmit the respective signals, and for one or other of these signalsto be demodulated selectively on the terminal side according to theradio wave propagation environment. It is also possible for execution ofboth OFDM modulation processing and OFDM-spreading modulation processingnot to be limited to an information signal directed to each station, butfor both to be executed, for example, on a common information signal forall terminals such as a broadcast signal and for the respective signalsto be transmitted, and for one or other of these signals to bedemodulated selectively on the terminal side according to the radio wavepropagation environment.

The configuration of a receiving system in this case is shown in FIG.76. FIG. 76, in which parts corresponding to those in FIG. 74 areassigned the same codes as in FIG. 74, shows the overall configurationof a terminal receiving system, which is similar to the configuration inFIG. 74 except for the provision of a selection section 7500 thatselects either demodulated data obtained by OFDM system demodulationsection 7306 or demodulated data obtained by OFDM-spreading systemdemodulation section 7307, based on the estimation result from radiowave propagation environment estimation section 7309.

That is to say, when the radio wave propagation: environment is poor,selection section 7500 selects information transmitted using theerror-resistant OFDM-spreading system, and when the radio wavepropagation environment is good, selection section 7500 selectsinformation transmitted using the OFDM modulation system, which offers ahigh transmission volume. By this means, it is possible to achieve bothan improvement in error rate characteristics and an increase in theamount of transmit data.

In this embodiment a case has been described in which execution of OFDMmodulation processing or execution of OFDM-spreading modulationprocessing is selected for an information signal directed to a terminalaccording to the radio wave propagation environment, but the presentinvention is not limited to a combination of OFDM modulation processingand OFDM-spreading modulation processing. For example, it is alsopossible to select execution of spreading processing or non-execution ofspreading processing for an information signal directed to a terminalaccording to the radio wave propagation environment, and for therespective signals to be transmitted multiplexed in the same frequencyband. In this case, also, if on the receiving side a spread signal isfirst demodulated, then a spread signal replica signal is formed, andthe replica signal is eliminated from the multiplex signal, a non-spreadsignal can be extracted, enabling both signals to be demodulated. As aresult, in this case also it is possible to achieve both an improvementin error rate characteristics and an increase in the amount of transmitdata by selecting a spread signal when the propagation environment ispoor and selecting a non-spread signal when the propagation environmentis good.

In this embodiment, a case has been described in which the radio wavepropagation environment is estimated by the receiving side that receivesa signal in which an OFDM modulated signal and OFDM-spreading modulatedsignal are multiplexed in the same frequency band, but the presentinvention is not limited to this, and the radio wave propagationenvironment may also be estimated by the transmitting side thattransmits an OFDM modulated signal and OFDM-spreading modulated signalmultiplexed in the same frequency band.

A transmitting apparatus according to the present invention has aconfiguration comprising a first modulation section that digitallymodulates an information signal and obtains a first modulated signal, asecond modulation section that digitally modulates a preset signalsequence and obtains a second modulated signal, a multiplexing sectionthat multiplexes the first modulated signal and second modulated signalin the same frequency band and obtains a multiplex signal, and atransmission section that transmits the multiplex signal.

A transmitting apparatus according to the present invention has aconfiguration in which a second modulation section digitally modulates apreset signal sequence by means of PSK modulation.

A transmitting apparatus according to the present invention has aconfiguration in which a preset signal sequence can be modified.

According to these configurations, since a transmitting apparatustransmits a first modulated signal and second modulated signalmultiplexed in the same frequency band, effective frequency utilizationcan be achieved. Also, by digitally modulating a preset signal sequenceby means of PSK modulation, it is possible to facilitate theconfiguration of a transmitting apparatus and receiving apparatus.Moreover, if a preset signal sequence is used as an encryption key,secure radio communication can be performed by modifying the signalsequence.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which a first modulated signal in which an information signalis digitally modulated and a second modulated signal in which a presetsignal sequence is digitally modulated are multiplexed in the samefrequency band, a synchronization section that acquires timesynchronization with the transmitting apparatus using the secondmodulated signal, and a demodulation section that demodulates the firstmodulated signal from the multiplex signal using synchronizationinformation obtained by the synchronization section.

According to this configuration, since the synchronization section canperform time synchronization based on the preset second modulatedsignal, it is not necessary to transmit separately a unique word orpilot signal for performing time synchronization. As a result,transmission of other information signals can be increasedcorrespondingly, enabling the data transmission speed to be improved.

A receiving apparatus according to the present invention has aconfiguration in which a demodulation section comprises a signalregeneration section that forms a replica signal of a second modulatedsignal by regenerating the second modulated signal within a multiplexsignal using synchronization information obtained by a synchronizationsection, and a signal elimination section that extracts the firstmodulated signal by eliminating the second modulated signal replicasignal from the multiplex signal.

According to this configuration, even when a first modulated signal inwhich an information signal is digitally modulated and a secondmodulated signal in which a preset signal sequence is digitallymodulated are multiplexed in the same frequency band, the firstmodulated signal and second modulated signal can be separatedsatisfactorily.

A receiving apparatus according to the present invention has aconfiguration in, which a signal regeneration section comprises a firstcode multiplication section that multiplies a multiplex signal by a codecorresponding to a second modulated signal, and a second codemultiplication section that forms a replica signal for the secondmodulated signal by again multiplying the signal after codemultiplication by the code corresponding to the second modulated signal.

According to this configuration, when a multiplex signal is multipliedin the first code multiplication section by a code corresponding to thesecond modulated signal at timing synchronized with the second modulatedsignal, only the second modulated signal is extracted from the multiplexsignal. Then a replica signal of the second modulated signal is formedby again multiplying by the code corresponding to the second modulatedsignal in the second code multiplication section. When this replicasignal is eliminated from the multiplex signal, the first modulatedsignal is extracted. Thus, by making the second modulated signal apreset signal sequence signal, it is possible to separate the firstmodulated signal and second modulated signal satisfactorily frommultiplexed signals multiplexed in the same frequency band.

A receiving apparatus according to the present invention has aconfiguration further comprising a low-pass filter that passes andsupplies to a second code multiplication section only a low-frequencyregion signal of signals after code multiplication by a first codemultiplication section.

According to this configuration, it is possible to eliminate a noisecomponent based on a first modulated signal contained in a signal aftercode multiplication by the first code multiplication section, enabling asecond modulated signal to be separated with significantly betterprecision. As a result, the quality of a replica signal of the secondmodulated signal also improves, and therefore the precision ofseparation of the first modulated signal also improves.

A receiving apparatus according to the present invention has aconfiguration comprising a pilot signal estimation section thatgenerates a pilot signal by multiplying a multiplex signal by a codecorresponding to a second modulated signal, and a coherent detectionsection that performs coherent detection of a first modulated signalextracted by a signal elimination section using the generated pilotsignal.

According to this configuration, a pilot signal is generated from thesecond modulated signal and used to perform first modulated signalcoherent detection, enabling the first modulated signal to bedemodulated with significantly better precision.

A receiving apparatus according to the present invention has aconfiguration whereby multiplex signals transmitted simultaneously froma plurality of transmitting apparatuses are received simultaneously,synchronization timing of the respective multiplex signals is detectedby a synchronization section, and a first modulated signal isdemodulated by a demodulation section by executing equalizationprocessing on the first modulated signal using the synchronizationtiming.

According to this configuration, even when multiplex signals in which afirst and second modulated signal are multiplexed in the same frequencyband are transmitted from a plurality of transmitting apparatuses, andpropagation delay differences occur due to differences in the distancesfrom the receiving apparatus to each transmitting apparatus, the firstmodulated signal can be demodulated with significantly better precisionby performing equalization processing using synchronization timingdetected based on a second modulation section when the first modulatedsignal is demodulated.

A receiving apparatus according to the present invention has aconfiguration whereby a preset signal sequence is held as confidentialinformation.

According to this configuration, if a preset signal sequence is notknown, a second modulated signal cannot be separated from a multiplexsignal, and therefore it is also impossible to obtain a first modulatedsignal. Thus, secure radio communication can be performed by using apreset signal sequence as an encryption key.

A transmitting apparatus according to the present invention has aconfiguration comprising a first modulation section that digitallymodulates an information signal and obtains a first modulated signal, asecond modulation section that digitally modulates an information signalby means of a spread spectrum system and obtains a second modulatedsignal, a multiplexing section that multiplexes the first modulatedsignal and second modulated signal in the same frequency band andobtains a multiplex signal, and a transmission section that transmitsthe multiplex signal.

According to this configuration, since a first modulated signal andsecond modulated signal are transmitted multiplexed in the samefrequency band, effective frequency utilization can be achieved. Also,the second modulated signal digitally modulated by means of a spreadspectrum system can be separated from the multiplex signal on thereceiving side by using the same spreading code as on the transmittingside.

A transmitting apparatus according to the present invention has aconfiguration in which a second modulation section obtains a pluralityof second modulated signals by spreading an information signal using aplurality of spreading codes.

According to this configuration, it is possible to make second modulatedsignals code division multiplexed signals using different spreadingcodes, thereby making it possible to greatly increase the quantity ofinformation signals multiplexed in the same frequency band, and enablingthe data transmission speed to be significantly improved.

A transmitting apparatus according to the present invention has aconfiguration whereby an information signal input to a second modulationsection is used as control information.

According to this configuration, a pilot signal or unique word or thelike, or control information for controlling a terminal or base stationnecessary for performing communication, is transmitted in a secondmodulated signal, making it unnecessary to insert control information ina first modulated signal. By this means a correspondingly greater amountof data can be transmitted in the first modulated signal, and the datatransmission speed can be improved.

A transmitting apparatus according to the present invention has aconfiguration whereby a spreading code used by a second modulationsection can be modified.

According to this configuration, secure radio communication can beperformed by using a spreading code as an encryption key and modifyingthe spreading code.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which a first modulated signal in which an information signalis digitally modulated and a second modulated signal in which aninformation signal is spread spectrum modulated are multiplexed in thesame frequency band, a spread spectrum demodulation section that obtainsa second modulated signal demodulated signal from the multiplex signalby despreading the second modulated signal, a spread spectrum modulatedsignal regeneration section that forms a replica signal of the secondmodulated signal by executing spreading processing on the signalobtained by the spread spectrum demodulation section, a signalelimination section that extracts the first modulated signal byeliminating the second modulated signal replica signal from themultiplex signal, and a demodulation section that demodulates theextracted first modulated signal.

According to this configuration, even when a first modulated signal inwhich an information signal is digitally modulated and a secondmodulated signal in which an information signal is spread spectrummodulated are multiplexed in the same frequency band, the firstmodulated signal and second modulated signal can be separatedsatisfactorily.

A receiving apparatus according to the present invention has aconfiguration wherein a second modulated signal is a code divisionmultiplexed signal obtained by performing spread spectrum processing ona plurality of information signals using different spreading codes; aspread spectrum demodulation section demodulates a code divisionmultiplexed plurality of signals by performing despreading processingusing a plurality of spreading codes on the multiplex signal; and aspread spectrum modulated signal regeneration section forms a replicasignal of the second modulated signal by executing spreading processingusing a plurality of spreading codes on the plurality of signalsobtained by the spread spectrum demodulation section.

According to this configuration, even when a second modulated signal isa signal code division multiplexed using a plurality of spreading codes,a first modulated signal and the second modulated signal can beseparated satisfactorily. Also, as the second modulated signal is a codedivision multiplexed signal, a significantly greater amount ofinformation can be obtained.

A receiving apparatus according to the present invention has aconfiguration further comprising a distortion estimation section thatestimates transmission path distortion of a multiplex signal using apilot signal received simultaneously with the multiplex signal, whereina spread spectrum modulated signal regeneration section forms a replicasignal to which the estimated transmission path distortion component hasbeen added.

According to this configuration, a replica signal can be made a signalwith the same kind of transmission path distortion as a multiplexsignal, enabling a first modulated signal to be extracted significantlymore satisfactorily by eliminating the replica signal from the multiplexsignal.

A transmitting apparatus according to the present invention has aconfiguration comprising a modulation section that digitally modulatesan information signal and obtains a modulated signal, a selectionsection that selects a signal corresponding to the information signalfrom a plurality of specific modulated signals, a multiplexing sectionthat multiplexes the modulated signal and the specific modulated signalselected by the selection section in the same frequency band and obtainsa multiplex signal, and a transmission section that transmits themultiplex signal.

According to this configuration, an information signal is transmittedvia a specific modulated signal, enabling the information signal to beestimated from the specific modulated signal on the receiving side. As aresult, it is possible to increase the amount of information that caneffectively be transmitted in the same frequency band. As the number ofspecific modulated signals is limited, if a correlation value is foundon the receiving side between a multiplex signal and specific modulatedsignals whose number is limited, for example, the specific modulatedsignal contained in the multiplex signal can easily be detected.

A transmitting apparatus according to the present invention has aconfiguration in which a selection section enables the correspondencebetween a selected specific modulated signal and an information signalto be modified.

According to this configuration, if the correspondence between aspecific signal and an information signal is used as an encryption key,secure radio communication can be performed by modifying thecorrespondence. That is to say, only a receiving apparatus thatrecognizes this correspondence can obtain the information signalcorresponding to a specific modulated signal.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which a modulated signal in which an information signal isdigitally modulated and a specific modulated signal selected ascorresponding to the information signal are multiplexed in the samefrequency band, a specific modulated signal estimation section thatestimates a specific modulated signal contained in the multiplex signaland outputs an information signal corresponding to that specificmodulated signal, a signal elimination section that extracts a modulatedsignal within the multiplex signal by eliminating a specific modulatedsignal from the multiplex signal, and a demodulation section thatdemodulates the extracted modulated signal.

According to this configuration, the specific modulated signalestimation section finds, for example, correlation values between aplurality of specific modulated signals and a multiplex signal andestimates a specific modulated signal contained in the multiplex signal,and obtains an information signal corresponding to the estimatedspecific modulated signal. The modulated signal is extracted by havingthe estimated specific modulated signal eliminated from the multiplexsignal by the signal elimination section. As a result, it is possible toobtain an information signal corresponding to a modulated signal and aninformation signal corresponding to a specific modulated signal frommultiplex signals multiplexed in the same frequency band.

A receiving apparatus according to the present invention has aconfiguration further comprising a distortion estimation section thatestimates transmission path distortion of a multiplex signal using pilotsymbols received simultaneously with the multiplex signal, wherein asignal elimination section eliminates a specific modulated signal towhich the estimated transmission path distortion component has beenadded from the multiplex signal.

According to this configuration, an estimated specific signal can bemade a signal that has the same kind of transmission path distort ion asa multiplex signal, so that a specific modulated signal to which adistortion component has been added is eliminated by a signalelimination section from a multiplex signal containing that distortioncomponent. As a result, a modulated signal can be extracted much moresatisfactorily.

A receiving apparatus according to the present invention has aconfiguration whereby information about correspondence betweena-specific modulated signal and information signal is received from atransmitting station, and a specific modulated signal estimation sectionoutputs an information signal corresponding to a specific modulatedsignal based on received correspondence information.

According to this configuration, only a receiving apparatus thatreceives the correspondence between a specific modulated signal andinformation signal can obtain an information signal corresponding to aspecific modulated signal. As a result, secure radio communication canbe performed.

A transmitting apparatus according to the present invention has aconfiguration comprising a first modulation section that digitallymodulates an information signal and obtains a first modulated signal, asecond modulation section that modulates an information signal using aspread spectrum system and obtains a second modulated signal, amultiplexing section that multiplexes the first modulated signal andsecond modulated signal in the same frequency band and obtains amultiplex signal, and a transmission section that transmits themultiplex signal; wherein the first and second modulation sectionsperform modulation processing so that signal points of the firstmodulated signal and the second modulated signal are arranged atdifferent positions in the in-phase-quadrature plane.

According to this configuration, since signal points of the firstmodulated signal and second modulated signal in the in-phase-quadratureplane are arranged differently, data errors can be suppressed whendemodulating each modulated signal. As a result, a transmit signal canbe transmitted at high speed and with good quality.

A transmitting apparatus according to the present invention has aconfiguration comprising a first modulation section that digitallymodulates an information signal and obtains a first modulated signal, asecond modulation section that modulates an information signal using aspread spectrum system and obtains a second modulated signal, amultiplexing section that multiplexes the first modulated signal andsecond modulated signal in the same frequency band and obtains amultiplex signal, and a transmission section that transmits themultiplex signal; wherein the second modulation section forms aplurality of spread information signals as second modulated signals byperforming spreading processing on signals subject to spreading usingdifferent spreading codes, and the multiplexing section multiplexesmultiplex frame information and/or spreading code information togetherwith the multiplex signal.

According to this configuration, multiplex frame or spreading codeinformation can be used as an encryption key, enabling securecommunication to be achieved.

A transmitting apparatus according to the present invention has aconfiguration comprising a first modulation section that digitallymodulates an information signal and obtains a first modulated signal, asecond modulation section that forms a plurality of Specific modulatedsignals modulated in a specific known arrangement decided beforehandwith the receiving side, a selection section that selects a signalcorresponding to the information signal from among the plurality ofspecific modulated signals, a multiplexing section that multiplexes thefirst modulated signal and the specific modulated signal selected by theselection section in the same frequency band and obtains a multiplexsignal, and a transmission section that transmits the multiplex signal;wherein the first and second modulation sections perform modulationprocessing so that signal points of the first modulated signal andspecific modulated signal are arranged at different positions in thein-phase-quadrature plane.

According to this configuration, an information signal is transmittedvia a specific modulated signal, enabling the information signal to beestimated from the specific modulated signal on the receiving side. As aresult, it is possible to increase the amount of information that can betransmitted in the same frequency band. As the number of specificmodulated signals is limited, the specific modulated signal contained inthe multiplex signal can easily be detected by sequentially finding acorrelation value on the receiving side between the multiplex signal andspecific modulated signals whose number is limited, for example. Also,since signal points of the first modulated signal and specific modulatedsignal in the in-phase-quadrature plane are arranged differently, dataerrors can be suppressed when demodulating each modulated signal.

A transmitting apparatus according to the present invention has aconfiguration comprising an OFDM modulation section that executesorthogonal frequency division multiplexing processing on an informationsignal and obtains an OFDM modulated signal, an OFDM-spreadingmodulation section that executes spreading processing and orthogonalfrequency division multiplexing processing on an information signal andobtains an OFDM-spreading modulated signal, a multiplexing section thatmultiplexes the OFDM modulated signal and OFDM-spreading modulatedsignal in the same frequency band and obtains a multiplex signal, and atransmission section that transmits the multiplex signal.

According to this configuration, since an OFDM modulated signal andOFDM-spreading modulated signal are transmitted multiplexed in the samefrequency band, effective frequency utilization can be achieved. Also,the OFDM-spreading modulated signal can be separated from the multiplexsignal on the receiving side by using the same spreading code as on thetransmitting side.

A transmitting apparatus according to the present invention has aconfiguration in which an OFDM modulation section and OFDM-spreadingmodulation section perform modulation processing so that signal pointsof the OFDM modulated signal and OFDM-spreading modulated signal arearranged at different positions in the in-phase-quadrature plane.

According to this configuration, since signal points of an OFDMmodulated signal and OFDM-spreading modulated signal in thein-phase-quadrature plane are arranged differently, data errors can besuppressed on the receiving side when demodulating each modulated signalafter separating each modulated signal.

A transmitting apparatus according to the present invention has aconfiguration in which a multiplexing Section multiplexes an OFDMmodulated signal and OFDM-spreading modulated signal in specificsubcarriers A transmitting apparatus according to the present inventionhas a configuration in which a multiplexing section multiplexes an OFDMmodulated signal and OFDM-spreading modulated signal in a specific timein a frame on the frequency-time axes.

According to these configurations, it is possible to increase only theamount of transmission information in a specific subcarrier or only theamount of transmission information for a specific time, enablingversatile communication to be performed.

A transmitting apparatus according to the present invention has aconfiguration whereby, in addition to an OFDM-modulated signal andOFDM-spreading modulated signal, information of a spreading code usedwhen performing OFDM-spreading modulation processing is multiplexed andtransmitted.

According to this configuration, an OFDM-spreading modulated signal canbe accurately separated from a multiplex signal and demodulated on thereceiving side based on spreading code information.

A transmitting apparatus according to the present invention has aconfiguration whereby an OFDM modulated signal and OFDM-spreadingmodulated signal are transmitted multiplexed in the same frequency bandat a specific time, and also either an OFDM modulated signal or anOFDM-spreading modulated signal is transmitted at a time other than thatspecific time.

According to this configuration, when it is wished to transmit a largeramount of information, for example, this information is transmitted as asignal multiplexed with an OFDM modulated signal and OFDM-spreadingmodulated signal at a specific time, and in the case of information forwhich it is wished to emphasize transmission quality rather than theamount of transmission information, this information is transmitted asan OFDM modulated signal or OFDM-spreading modulated signal at a timeother than the specific time. As a result, it is possible to performcommunication with greater diversity.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which a first modulated signal in which an information signalis digitally modulated and a second modulated signal in which aninformation signal is modulated using a spread spectrum system and whosesignal points are arranged at different positions from those of thefirst modulated signal in the in-phase-quadrature plane are multiplexedin the same frequency band, a despreading and demodulation section thatdespreads the received multiplex signal and also demodulates the secondmodulated signal taking account of the signal point arrangement at thetime of modulation, a regeneration section that regenerates the secondmodulated signal from the demodulated signal and forms a replica signalof the second modulated signal, a signal elimination section thatextracts the first modulated signal by eliminating the replica signalfrom the received multiplex signal, and a demodulation section thatdemodulates the extracted first modulated signal taking account of thesignal point arrangement at the time of modulation.

According to this configuration, when the first modulated signal isdemodulated by the despreading and demodulation section, and when thesecond modulated signal is demodulated by the despreading section, onemodulated signal has different signal point positions from the othermodulated signal, and therefore even when the other modulated signalcomponent remains when one modulated signal is demodulated, that onemodulated signal can be demodulated with good precision.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which a first modulated signal in which an information signalis digitally modulated and a second modulated signal formed byperforming spreading processing on information signals subject tospreading using different spreading codes are multiplexed in the samefrequency band, and multiplex frame information and/or spreading codeinformation; a despreading and demodulation section that despreads thereceived multiplex signal using different spreading codes anddemodulates each spread information signal; a regeneration section thatforms a second modulated signal replica signal by regenerating a secondmodulated signal from each demodulated information signal; a signalelimination section that extracts the first modulated signal byeliminating the second modulated signal replica signal from the receivedmultiplex signal at predetermined timing; and a demodulation sectionthat demodulates the extracted first modulated signal; wherein thedespreading and demodulation section and/or signal elimination sectionperforms despreading and demodulation processing and/or signalelimination processing based on received multiplex frame informationand/or spreading code information.

According to this configuration, it is possible to perform secondmodulated signal despreading processing by means of the despreading anddemodulation section based on multiplex frame information or spreadingcode information, satisfactorily perform processing for replica signalelimination from a multiplex signal by means of the signal eliminationsection, and separate and demodulate a second modulated signal and firstmodulated signal with good quality.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which an OFDM modulated signal resulting from execution ofOFDM modulation processing on an information signal and anOFDM-spreading modulated signal resulting from execution ofOFDM-spreading modulation processing on an information signal aremultiplexed in the same frequency band, a first demodulation sectionthat demodulates the OFDM-spreading modulated signal within themultiplex signal, a regeneration section that forms a replica signal ofthe OFDM-spreading modulated signal by regenerating the OFDM-spreadingmodulated signal from the demodulated signal, a signal eliminationsection that extracts the OFDM modulated signal by eliminating theOFDM-spreading modulated signal replica signal from the receivedmultiplex signal, and a second demodulation section that demodulates theextracted OFDM modulated signal.

According to this configuration, an OFDM modulated signal can beseparated from a multiplex signal by first separating and demodulatingan OFDM-spreading modulated signal from the multiplex signal by means ofthe first demodulation section using a spreading code, and theneliminating the OFDM-spreading modulated signal replica signal formed bythe regeneration section from the multiplex signal in the signalelimination section. By this means, it is possible to separate anddemodulate an OFDM modulated signal and OFDM-spreading modulated signalmultiplexed in the same frequency band.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which an OFDM modulated signal resulting from execution ofOFDM modulation processing on an information signal and anOFDM-spreading modulated signal resulting from execution ofOFDM-spreading modulation processing on an information signal aremultiplexed in the same frequency band, and information of a spreadingcode used when performing OFDM-spreading modulation processing; a firstdemodulation section that demodulates the OFDM-spreading modulatedsignal within the multiplex signal based on the spreading codeinformation; a regeneration section that forms a replica signal of theOFDM-spreading modulated signal by regenerating the OFDM-spreadingmodulated signal from the demodulated signal; a signal eliminationsection that extracts the OFDM modulated signal by eliminating theOFDM-spreading modulated signal replica signal from the receivedmultiplex signal; and a second demodulation section that demodulates theextracted OFDM modulated signal.

According to this configuration, a spreading code used when the firstdemodulation section separates an OFDM-spreading modulated signal from amultiplex signal is received from the transmitting side, so that onlythe specific receiving apparatus that receives this spreading code canseparate and demodulate an OFDM modulated signal and OFDM-spreadingmodulated signal from a multiplex signal, enabling secure communicationto be achieved.

A receiving apparatus according to the present invention has aconfiguration further comprising a distortion estimation section thatestimates transmission path distortion based on a known signal in areceived multiplex signal; wherein a regeneration section forms areplica signal of an OFDM-spreading modulated signal to which theestimated transmission path distortion component has been added.

According to this configuration, a replica signal can be made a signalthat has the same kind of transmission path distortion as a receivedmultiplex signal, so that an OFDM modulated signal can be extracted farmore satisfactorily by having a signal elimination section eliminate areplica signal to which a distortion component has been added from areceived multiplex signal containing a distortion component.

A transmitting apparatus according to the present invention has aconfiguration comprising a first spreading section that obtains a firstspread signal by spreading an information signal using a first spreadingcode that has a first spreading ratio, a second spreading section thatobtains a second spread signal by spreading an information signal usinga second spreading code that has a second spreading ratio different fromthe first spreading ratio, a multiplexing section that obtains amultiplex signal by multiplexing the first spread signal and secondspread signal in the same frequency band, and a transmission sectionthat transmits the multiplex signal.

According to this configuration, since a first spread signal and secondspread signal with different spreading ratios are transmittedmultiplexed in the same frequency band, effective frequency utilizationcan be achieved. Also, spread signals with different spreading ratioscan be separated from a multiplex signal by using spreading codes withdifferent spreading ratios on the receiving side.

A transmitting apparatus according to the present invention has aconfiguration comprising a first OFDM-spreading modulation section thatobtains a first OFDM-spreading modulated signal by performing spreadingprocessing using a first spreading code that has a first spreading ratioand orthogonal frequency division multiplexing processing on aninformation signal, a second OFDM-spreading modulation section thatobtains a second OFDM-spreading modulated signal by performing spreadingprocessing using a second spreading code that has a second spreadingratio different from the first spreading ratio and orthogonal frequencydivision multiplexing processing on an information signal, amultiplexing section that obtains a multiplex signal by multiplexing thefirst OFDM-spreading modulated signal and second OFDM-spreadingmodulated signal in the same frequency band, and a transmission sectionthat transmits the multiplex signal.

According to this configuration, since first and second OFDM-spreadingmodulated signals are transmitted multiplexed in the same frequencyband, effective frequency utilization can be achieved. Also, twoOFDM-spreading modulated signals with different spreading ratios can beseparated from a multiplex signal by using spreading codes withdifferent spreading ratios on the receiving side.

A transmitting apparatus according to the present invention has aconfiguration whereby the transmission power of a second modulatedsignal is made greater than the transmission power of a first modulatedsignal.

According to this configuration, the correlation between a firstmodulated signal and second modulated signal can be made small, enablingeach signal to be separated from a multiplex signal with significantlybetter precision on the receiving side. Also, when the second modulatedsignal with the larger transmission power is separated from themultiplex signal before the second modulated signal on the receivingside, the precision of separation of the second modulated signalseparated first can be improved, enabling the precision of separation ofthe first modulated signal extracted by subtracting a replica signal ofthe second modulated signal from the multiplex signal also to beimproved.

A transmitting apparatus according to the present invention has aconfiguration whereby the transmission power of an OFDM-spreadingmodulated signal is made greater than the transmission power of an OFDMmodulated signal.

According to this configuration, the correlation between anOFDM-spreading modulated signal and OFDM modulated signal can be madesmall, enabling each signal to be separated from a multiplex signal withsignificantly better precision on the receiving side. Also, theOFDM-spreading modulated signal is separated from the multiplex signalbefore the OFDM modulated signal on the receiving side, and as thetransmission power of the OFDM-spreading modulated signal separatedfirst is greater at this time, the OFDM-spreading modulated signal canbe separated with good precision. Therefore, the precision of separationof an OFDM modulated signal extracted by subtracting a replica signal ofthe OFDM-spreading modulated signal from the multiplex signal can alsobe improved.

A transmitting apparatus according to the present invention has aconfiguration whereby the transmission power of whichever of a first orsecond spread signal is spread using a spreading code with a largerspreading ratio is made greater than the transmission power of the otherspread signal.

According to this configuration, the correlation between a first spreadsignal and second spread signal can be made small, enabling each spreadsignal to be separated from a multiplex signal with significantly betterprecision on the receiving side. Also, when the spread signal with thelarger spreading ratio is separated first from the multiplex signal onthe receiving side, as the transmission power of this spread signal withthe larger spreading ratio is greater than the transmission power of theother spread signal, the spread signal with the larger spreading ratiocan be separated from the multiplex signal with good precision.Therefore, the precision of separation of the spread signal with thesmaller spreading ratio extracted by subtracting a replica signal of thespread signal with the larger spreading ratio from the multiplex signalcan also be improved.

A transmitting apparatus according to the present invention has aconfiguration whereby, of a first and second OFDM-spreading modulatedsignal, the transmission power of the OFDM-spreading modulated signalformed using the spreading code with the larger spreading ratio is madegreater than the transmission power of the other OFDM-spreadingmodulated signal.

According to this configuration, the correlation between a firstOFDM-spreading modulated signal and second OFDM-spreading modulatedsignal can be made small, enabling each OFDM-spreading modulated signalto be separated from a multiplex signal with significantly betterprecision on the receiving side. Also, when the OFDM-spreading modulatedsignal with the larger spreading ratio is separated first from themultiplex signal on the receiving side, as the transmission power ofthis OFDM-spreading modulated signal with the larger spreading ratio isgreater than the transmission power of the other OFDM-spreadingmodulated signal, the OFDM-spreading modulated signal with the largerspreading ratio can be separated from the multiplex signal with goodprecision. Therefore, the precision of separation of the OFDM-spreadingmodulated signal with the smaller spreading ratio extracted bysubtracting a replica signal of the OFDM-spreading modulated signal withthe larger spreading ratio from the multiplex signal can also beimproved.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which first and second spread spectrum signals formed usingspreading codes with different spreading ratios on an information signalare multiplexed in the same frequency band, a first demodulation sectionthat separates and demodulates the first spread spectrum signal from thereceived multiplex signal using a spreading code corresponding to thefirst spread spectrum signal, a regeneration section that forms areplica signal of the first spread spectrum signal by regenerating thefirst spread spectrum signal from the demodulated signal, a signalelimination section that extracts the second spread spectrum signal byeliminating the first spread spectrum signal replica signal from thereceived multiplex signal, and a second demodulation section thatdemodulates the extracted second spread spectrum signal.

According to this configuration, a first spread spectrum signal can beseparated and demodulated from a received multiplex signal by means ofdespreading processing by the first demodulation section. Also, a secondspread spectrum signal can be separated by eliminating the first spreadspectrum signal component from the received multiplex signal by means ofthe signal elimination section. Thus, spread spectrum signals withdifferent spreading ratios can be separated from a received multiplexsignal and demodulated.

A receiving apparatus according to the present invention has aconfiguration whereby a first spread spectrum signal is a spreadspectrum signal with a larger spreading ratio than a second spreadspectrum signal, and demodulation is performed in order from the spreadspectrum signal with the larger spreading ratio.

According to this configuration, attention is paid to the fact that,when spread signals with different spreading ratios are multiplexed,despreading precision is higher for the spread signal with the largerspreading ratio, and separation and demodulation are performed within areceived multiplex signal in order from the spread signal with thelarger spreading ratio. As a result, the precision of separation of aspread signal next extracted by subtracting a replica signal from themultiplex signal is also improved, enabling all spread signals to beseparated and demodulated with good precision.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which first and second OFDM-spreading modulated signals formedusing spreading codes with different spreading ratios on an informationsignal and executing orthogonal frequency division multiplexing on thesignals after spreading are multiplexed in the same frequency band, afirst demodulation section that separates and demodulates the firstOFDM-spreading modulated signal from the received multiplex signal usinga spreading code corresponding to the first OFDM-spreading modulatedsignal, a regeneration section that forms a replica signal of the firstOFDM-spreading modulated signal by regenerating the first OFDM-spreadingmodulated signal from the demodulated signal, a signal eliminationsection that extracts the second OFDM-spreading modulated signal byeliminating the first OFDM-spreading modulated signal replica signalfrom the received multiplex signal, and a second demodulation sectionthat demodulates the extracted second OFDM-spreading modulated signal.

According to this configuration, a first OFDM-spreading modulated signalcan be separated and demodulated from a received multiplex signal bymeans of despreading processing by the first demodulation section. Also,a second OFDM-spreading modulated signal can be separated by eliminatingthe first OFDM-spreading modulated signal component from the receivedmultiplex signal by means of the signal elimination section. Thus,OFDM-spreading modulated signals formed using spreading codes withdifferent spreading ratios can be separated from a received multiplexsignal and demodulated.

A receiving apparatus according to the present invention has aconfiguration whereby a first OFDM-spreading modulated signal is anOFDM-spreading modulated signal formed using a spreading code with alarger spreading ratio than a second OFDM-spreading modulated signal,and demodulation is performed in order from the OFDM-spreading modulatedsignal formed using the spreading code with the larger spreading ratio.

According to this configuration, attention is paid to the fact that,when OFDM-spreading modulated signals with different spreading ratiosare multiplexed, despreading precision is higher for the OFDM-spreadingmodulated signal with the larger spreading ratio, and separation anddemodulation are performed within a received multiplex signal in orderfrom the OFDM-spreading modulated signal with the higher spreadingratio. As a result, the precision of separation of an OFDM-spreadingmodulated signal next extracted by subtracting a replica signal from themultiplex signal is also improved, enabling all OFDM-spreading modulatedsignals to be separated and demodulated with good precision.

A transmitting apparatus according to the present invention has aconfiguration comprising a first modulation section that obtains aspread signal by modulating an information signal using a spreadspectrum system; a second modulation section that obtains a non-spreadsignal by modulating an information signal not using a spread spectrumsystem; a modulation selection section that, based on the propagationpath environment of the transmission target station, selects the firstmodulation section and has spreading processing performed on aninformation signal directed to that transmission target station when thepropagation path environment is poor, and selects the second modulationsection and does not have spreading processing performed on aninformation signal directed to that transmission target station when thepropagation environment is good; a multiplexing section that multiplexesa plurality of modulated signals that have undergone modulationprocessing by means of the selected modulation system in the samefrequency band and obtains a multiplex signal; and a transmissionsection that transmits the multiplex signal.

According to this configuration, spread signals with good resistance toerrors are transmitted multiplexed in the same frequency band to atransmission target station when the propagation environment is poor,and non-spread signals with a large transmission capacity aretransmitted multiplexed in the same frequency band to a transmissiontarget station when the propagation environment is good, making itpossible to achieve both an improvement in error rate characteristicsand an increase in the amount of transmit data.

A transmitting apparatus according to the present invention has aconfiguration comprising an OFDM modulation section that executesorthogonal frequency division multiplexing processing on an informationsignal and obtains an OFDM modulated signal; an OFDM-spreadingmodulation section that executes spreading processing and orthogonalfrequency division multiplexing processing on an information signal andobtains an OFDM-spreading modulated signal; a modulation selectionsection that, based on the propagation path environment of thetransmission target station, selects the OFDM-spreading modulationsection and has spreading processing and orthogonal frequency divisionmultiplexing processing executed on an information signal directed tothat transmission target station when the propagation path environmentis poor, and selects the OFDM modulation section and has orthogonalfrequency division multiplexing executed on an information signaldirected to that transmission target station when the propagationenvironment is good; a multiplexing section that multiplexes a pluralityof modulated signals that have undergone modulation processing by meansof the selected modulation system in the same frequency band and obtainsa multiplex signal; and a transmission section that transmits themultiplex signal.

According to this configuration, OFDM-spreading modulated signals withgood resistance to errors are transmitted multiplexed in the samefrequency band to a transmission target station when the propagationenvironment is poor, and OFDM modulated signals with a largetransmission capacity are transmitted multiplexed in the same frequencyband to a transmission target station when the propagation environmentis good, making it possible to achieve both an improvement in error ratecharacteristics and an increase in the amount of transmit data.

A transmitting apparatus according to the present invention has aconfiguration comprising a first modulation section that obtains aspread signal by modulating an information signal using a spreadspectrum system, and a second modulation section that obtains anon-spread signal by modulating an information signal not using a spreadspectrum system; wherein by executing processing by the first and secondmodulation sections on the same information signal, a spread signal andnon-spread signal are obtained for the same information signal, and thatspread signal and non-spread signal are transmitted multiplexed in thesame frequency band.

According to this configuration, it is possible to obtain an informationsignal by selecting a spread signal with good resistance to errors or anon-spread signal with a large transmission capacity on the receivingside according to the radio wave propagation environment, as a result ofwhich a large amount of information can be obtained.

A transmitting apparatus according to the present invention has aconfiguration comprising an OFDM modulation section that obtains an OFDMmodulated signal by executing orthogonal frequency division multiplexingprocessing on an information signal, and an OFDM-spreading modulationsection that obtains an OFDM-spreading modulated signal by executingspreading processing and orthogonal frequency division multiplexingprocessing on an information signal; wherein by executing processing bythe OFDM modulation section and OFDM-spreading modulation section on thesame information signal, an OFDM modulated signal and OFDM-spreadingmodulated signal are obtained for the same information signal, and thatOFDM modulated signal and OFDM-spreading modulated signal aretransmitted multiplexed in the same frequency band.

According to this configuration, it is possible to obtain an informationsignal by selecting an OFDM-spreading modulated signal with goodresistance to errors or an OFDM modulated signal with a largetransmission capacity on the receiving side according to the radio wavepropagation environment, as a result of which a large amount ofinformation can be obtained.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which a spread signal and non-spread signal for the sameinformation signal are multiplexed in the same frequency band, adespreading and demodulation section that demodulates the spread signalin the multiplex signal by despreading the received multiplex signal, aregeneration section that regenerates a spread signal from thedemodulated signal and forms a replica signal of the spread signal, asignal elimination section that extracts the non-spread signal byeliminating the replica signal from the received multiplex signal, ademodulation section that demodulates the extracted non-spread signal, aradio wave propagation environment estimation section that estimates theradio wave propagation environment between the receiving apparatus andthe transmitting station, and a selection section that selects eitherthe demodulated spread signal or the demodulated non-spread signal basedon the estimated radio wave propagation environment.

According to this configuration, it is possible to select an informationsignal transmitted using a spread signal with good resistance to errorswhen the propagation environment is poor, and to select an informationsignal transmitted using a non-spread signal with a large transmissioncapacity when the propagation environment is good, as a result of whicha large amount of information can be obtained.

A receiving apparatus according to the present invention has aconfiguration comprising a reception section that receives a multiplexsignal in which an OFDM modulated signal and an OFDM-spreading modulatedsignal for the same information signal are multiplexed in the samefrequency band, a first demodulation section that demodulates theOFDM-spreading modulated signal in the received multiplex signal, aregeneration section that regenerates an OFDM-spreading modulated signalfrom the demodulated OFDM-spreading modulated signal and forms a replicasignal of the OFDM-spreading modulated signal, a signal eliminationsection that extracts the OFDM modulated signal by eliminating thereplica signal from the received multiplex signal, a second demodulationsection that demodulates the extracted OFDM modulated signal, a radiowave propagation environment estimation section that estimates the radiowave propagation environment between the receiving apparatus and thetransmitting station, and a selection section that selects either thedemodulated OFDM modulated signal or the demodulated OFDM-spreadingmodulated signal based on the estimated radio wave propagationenvironment.

According to this configuration, it is possible to select an informationsignal transmitted using an OFDM-spreading modulated signal with goodresistance to errors when the propagation environment is poor, and toselect an information signal transmitted using an OFDM modulated signalwith a large transmission capacity when the propagation environment isgood, as a result of which a large amount of information can beobtained.

In a radio communication method according to the present invention, atransmitting apparatus multiplexes in the same frequency band andtransmits a first modulated signal obtained by digitally modulating aninformation signal and a second modulated signal obtained by digitallymodulating a preset signal sequence, and a receiving apparatusdemodulates the second modulated signal from the multiplex signal usinga preset signal sequence, forms a replica signal of the second modulatedsignal based on the demodulated signal, extracts the first modulatedsignal by eliminating the replica signal of the second modulated signalfrom the multiplex signal, and demodulates the extracted first modulatedsignal.

According to this method, even when a first modulated signal in which aninformation signal is digitally modulated and a second modulated signalin which a preset signal sequence is digitally modulated are multiplexedin the same frequency band, the first modulated signal and secondmodulated signal can be separated satisfactorily.

In a radio communication method according to the present invention, atransmitting apparatus multiplexes in the same frequency band andtransmits a first modulated signal obtained by digitally modulating aninformation signal and a second modulated signal obtained by digitallymodulating an information signal by means of a spread spectrum system,and a receiving apparatus demodulates the second modulated signal byperforming spread spectrum demodulation on the received multiplexsignal, performs spread spectrum processing on the demodulated secondmodulated signal and forms a replica signal of the second modulatedsignal, extracts the first modulated signal by eliminating the replicasignal of the second modulated signal from the received multiplexsignal, and demodulates the extracted first modulated signal.

According to this method, even when a first modulated signal in which aninformation signal is digitally modulated and a second modulated signalin which an information signal is digitally modulated by means of aspread spectrum system are multiplexed in the same frequency band, thefirst modulated signal and second, modulated signal can be separatedsatisfactorily.

In a radio communication method according to the present invention, atransmitting apparatus multiplexes in the same frequency band andtransmits a modulated signal obtained by digitally modulating aninformation signal and a specific signal corresponding to theinformation signal selected from a plurality of specific signals, and areceiving apparatus identifies the specific signal contained in thereceived multiplex signal, and obtains the aforementioned modulatedsignal by eliminating the identified specific signal from the receivedmultiplex signal.

According to this configuration, an information signal is transmittedvia a specific modulated signal, enabling the information signal to beestimated from the specific modulated signal on the receiving side. As aresult, it is possible to increase the amount of information that can betransmitted in the same frequency band. As the number of specificmodulated signals is limited, the specific modulated signal contained inthe multiplex signal can easily be detected by sequentially finding acorrelation value on the receiving side between the multiplex signal andspecific modulated signals whose number is limited, for example.

In a radio communication method according to the present invention,a-transmitting apparatus multiplexes in the same frequency band andtransmits an OFDM modulated signal obtained by performing orthogonalfrequency division multiplexing processing on an information signal andan OFDM-spreading modulated signal obtained by performing spreadingprocessing and orthogonal frequency division multiplexing processing onan information signal, and a receiving apparatus extracts theOFDM-spreading modulated signal by executing OFDM-spreading modulationprocessing on the received multiplex signal, forms a replica signal ofthe OFDM-spreading modulated signal by regenerating the extractedOFDM-spreading modulated signal, and obtains the OFDM modulated signalby eliminating the replica signal of the OFDM-spreading modulated signalfrom the received multiplex signal.

According to this method, an OFDM modulated signal can be separated froma multiplex signal by first separating and demodulating anOFDM-spreading modulated signal from the multiplex signal using aspreading code, and then eliminating a replica signal of theOFDM-spreading modulated signal from the multiplex signal. By thismeans, it is possible to separate and demodulate an OFDM modulatedsignal and OFDM-spreading modulated signal multiplexed in the samefrequency band. As a result, it is possible to achieve effectivefrequency utilization and implement large-volume communication.

In a radio communication method according to the present invention, atransmitting apparatus multiplexes in the same frequency band andtransmits first and second spread signals formed using first and secondspreading codes with different spreading ratios, and a receivingapparatus demodulates the first spread signal from the receivedmultiplex signal using a spreading code corresponding to the firstspread signal, forms a replica signal of the first spread signal byregenerating the first spread signal from the demodulated signal, andobtains the second spread signal by eliminating the replica signal fromthe received multiplex signal.

According to this method, a first spread spectrum signal is firstseparated and demodulated from a received multiplex signal by means ofdespreading processing using a first spreading code, then a secondspread spectrum signal is separated by eliminating the replica signal ofthe first spread spectrum signal from the received multiplex signal. Itis thus possible to separate and demodulate spread spectrum signals withdifferent spreading ratios from a received multiplex signal. As aresult, it is possible to achieve effective frequency utilization andimplement large-volume communication.

In a radio communication method according to the present invention, atransmitting apparatus multiplexes in the same frequency band andtransmits first and second OFDM-spreading modulated signals formed usingfirst and second spreading codes with different spreading ratios, and areceiving apparatus demodulates the first OFDM-spreading modulatedsignal from the received multiplex signal using a spreading codecorresponding to the first OFDM-spreading modulated signal, generates areplica signal of the first OFDM-spreading modulated signal byregenerating the first OFDM-spreading modulated signal from thedemodulated signal, and obtains the second OFDM-spreading modulatedsignal by eliminating the replica signal from the received multiplexsignal.

According to this method, a first OFDM-spreading modulated signal isfirst separated and demodulated from a received multiplex signal bymeans of despreading processing using a first spreading code, then asecond OFDM-spreading modulated signal is separated by eliminating thereplica signal of the first OFDM-spreading modulated signal from thereceived multiplex signal. It is thus possible to separate anddemodulate OFDM-spreading modulated signals with different spreadingratios from a received multiplex signal. As a result, it is possible toachieve effective frequency utilization and implement large-volumecommunication.

In a radio communication method according to the present invention, areceiving apparatus performs demodulation sequentially from a signalobtained using a spreading code with a large spreading ratio amongsignals contained in a received multiplex signal.

According to this method, attention is paid to the fact that despreadingprecision is higher for a spread signal with a larger spreading ratio,and separation and demodulation are performed within a receivedmultiplex signal in order from the spread signal with the largestspreading ratio. As a result, the precision of separation of a spreadsignal next extracted by subtracting a replica signal from the multiplexsignal is also improved, enabling all spread signals to be separated anddemodulated with good precision.

In a radio communication method according to the present invention, areceiving apparatus performs demodulation sequentially from a signalwith large reception power among signals contained in a receivedmultiplex signal.

According to this method, attention is paid to the fact that precisionat the time of separation from a multiplex signal is higher for a signalwith larger reception power, and separation and demodulation areperformed within a received multiplex signal in order from the signalwith the largest reception power. As a result, the precision ofseparation of a signal next extracted by subtracting a replica signalfrom the multiplex signal is also improved, enabling all signals to beseparated and demodulated with good precision.

In a radio communication method according to the present invention, atransmitting apparatus obtains a spread signal and non-spread signalfrom the same signal, and transmits these signals-multiplexed in thesame frequency band, and a receiving apparatus estimates the radio wavepropagation environment between the receiving apparatus and thetransmitting apparatus, and selects and demodulates either the spreadsignal or the non-spread signal from the received multiplex signal basedon the estimated radio wave propagation environment.

According to this method, a large amount of information can be obtainedif an information signal transmitted using a spread signal with goodresistance to errors is selected when the propagation environment ispoor, and an information signal transmitted using a non-spread signalwith a large transmission capacity is selected when the propagationenvironment is good.

In a radio communication method according to the present invention, atransmitting apparatus obtains an OFDM signal and OFDM-spread signalfrom the same signal, and transmits these signals multiplexed in thesame frequency band, and a receiving apparatus estimates the radio wavepropagation environment between the receiving apparatus and thetransmitting apparatus, and selects and demodulates either the OFDMsignal or the OFDM-spread signal from the received multiplex signalbased on the estimated radio wave propagation environment.

According to this method, a large amount of information can be obtainedif an information signal transmitted using an OFDM-spread signal withgood resistance to errors is selected when the propagation environmentis poor, and an information signal transmitted using an OFDM signal witha large transmission capacity is selected when the propagationenvironment is good.

As described above, according to the present invention, by transmittinga plurality of digitally modulated signals multiplexed in the samefrequency band, the data transmission amount per unit time can beincreased, enabling the data transmission speed to be improved.

This application is based on Japanese Patent Application No. 2001-244929filed on Aug. 10, 2001, Japanese Patent Application No. 2001-310777filed on Oct. 5, 2001, and Japanese Patent Application No. 2002-206150filed on Jul. 15, 2002, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a transmitting apparatus,receiving apparatus, and radio communication method whereby a greateramount of data is transmitted in a limited frequency band.

1. A transmitting apparatus comprising: an OFDM modulator that generatesa first modulation symbol by modulating a first information signal usinga first modulation scheme, a signal point of the first modulatedinformation signal being arranged at a first position in an in-phasequadrature-phase plane, a second modulation symbol by modulating asecond information signal using the first modulation scheme, and bychanging a second position at which a signal point of the modulatedsecond information signal is arranged to a third position in thein-phase quadrature-phase plane, wherein the third position is differentfrom the first position, and an OFDM modulation signal including thefirst modulation symbol and the second modulation symbol, wherein theOFDM modulation signal comprises a plurality of subcarriers′, and atransmitter that transmits the OFDM modulation signal.
 2. Thetransmitting apparatus according to claim 1, wherein the firstmodulation symbol and the second modulation symbol are arranged in asame subcarrier in the OFDM modulation signal.
 3. A transmission methodcomprising: generating a first modulation symbol by modulating a firstinformation signal using a first modulation scheme, a signal point ofthe first modulated information signal being arranged at a firstposition in an in-phase quadrature-phase plane; generating a secondmodulation symbol by modulating a second information signal using thefirst modulation scheme, and by changing a second position at which asignal point of the second modulated information signal is arranged to athird position in the in-phase quadrature phase plane, wherein the thirdposition is different from the first position, and generating an OFDMmodulation signal including the first modulation symbol and the secondmodulation symbol, wherein the OFDM modulation signal comprises aplurality of subcarriers′, and transmitting the OFDM modulation signal.4. The transmission method according to claim 3, wherein the firstmodulation symbol and the second modulation symbol are arranged in asame subcarrier in the OFDM modulation signal.
 5. A reception apparatuscomprising: a receptor that receives an OFDM modulation signal to whicha first modulation symbol and a second modulation symbol aremultiplexed, wherein the OFDM modulation signal comprises a plurality ofsubcarriers, the plurality of subcarriers include the first modulationsymbol arranged in a first position in an in-phase quadrature-phaseplane, and the second modulation symbol arranged in a third position inthe in-phase quadrature-phase plane, the first modulation symbol is asymbol to which a first information signal is modulated using a firstmodulation scheme, the second modulation symbol is a symbol obtained bymodulating a second information signal using the first modulationscheme, and by changing a second position at which a signal point of thesecond modulated information signal is arranged to the third position inthe in-phase quadrature-phase plane; and a demodulator that separatesthe first modulation symbol and the second modulation symbol included inthe OFDM signal, demodulates the first information signal from the firstmodulation symbol, and demodulates the second information signal fromthe second modulation symbol.
 6. The reception apparatus according toclaim 5, wherein the first modulation symbol and the second modulationsymbol are arranged in a same subcarrier in the received OFDM modulationsignal.
 7. A reception method comprising: receiving an OFDM modulationsignal to which a first modulation symbol and a second modulation symbolare multiplexed, wherein the OFDM modulation signal comprises aplurality of subcarriers, the plurality of subcarriers include the firstmodulation symbol arranged in a first position in an in-phasequadrature-phase plane, and the second modulation symbol arranged in athird position in the in-phase quadrature-phase plane, the firstmodulation symbol is a symbol to which a first information signal ismodulated using a first modulation scheme, the second modulation symbolis a symbol obtained by modulating a second information signal using thefirst modulation scheme, and by changing a second position at which asignal point of the second modulated information signal is arranged tothe third position in the in-phase quadrature-phase plane; separatingthe first modulation symbol and the second modulation symbol included inthe OFDM signal′, demodulating the first information signal from thefirst modulation symbol′, and demodulating the second information signalfrom the second modulation symbol.
 8. The reception method according toclaim 7, wherein the first modulation symbol and the second modulationsymbol are arranged in a same subcarrier in the received OFDM modulationsignal.